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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<title>SysDesign.track — Beginner to Advanced</title>
<link href="https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600&family=Outfit:wght@400;500;600;700&display=swap" rel="stylesheet"/>
<style>
:root {
--bg:#040404; --bg2:#080808; --bg3:#0d0d0d;
--s1:#101010; --s2:#161616; --s3:#1e1e1e;
--green:#3ddc84; --green2:#2bbd6e; --green3:#1a5c38;
--gdim:rgba(61,220,132,.07); --gglow:0 0 20px rgba(61,220,132,.12);
--amber:#f5a623; --adim:rgba(245,166,35,.08);
--red:#f06565; --rdim:rgba(240,101,101,.08);
--blue:#6eb5ff; --bdim:rgba(110,181,255,.08);
--purple:#a78bfa; --pdim:rgba(167,139,250,.08);
--cyan:#22d3ee; --cdim:rgba(34,211,238,.08);
--text:#d0d0d0; --t2:#6a6a6a; --t3:#3a3a3a;
--brd:#181818; --brd2:#242424;
--sans:'Inter',sans-serif; --disp:'Outfit',sans-serif;
--r:8px; --rs:5px;
}
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
body{background:var(--bg);color:var(--text);font-family:var(--sans);font-size:14px;min-height:100vh;-webkit-font-smoothing:antialiased;overflow-x:hidden}
/* ── HEADER ── */
.hdr{border-bottom:1px solid var(--brd);padding:15px 32px;display:flex;align-items:center;justify-content:space-between;background:rgba(8,8,8,.95);position:sticky;top:0;z-index:200;backdrop-filter:blur(20px)}
.logo{display:flex;align-items:center;gap:12px}
.logo-ico{width:34px;height:34px;background:var(--gdim);border:1px solid rgba(61,220,132,.2);border-radius:var(--rs);display:flex;align-items:center;justify-content:center;font-size:16px}
.logo-name{font-family:var(--disp);font-size:18px;font-weight:700;color:#e8e8e8;letter-spacing:-.3px}
.logo-name span{color:var(--green)}
.logo-tag{font-size:10px;color:var(--t3);letter-spacing:1px;margin-top:2px}
.hdr-pills{display:flex;gap:8px;align-items:center}
.pill{display:flex;align-items:center;gap:6px;background:var(--s1);border:1px solid var(--brd2);border-radius:20px;padding:5px 14px;font-size:12px;color:var(--t2)}
.dot{width:7px;height:7px;border-radius:50%;flex-shrink:0}
.dg{background:var(--green)} .da{background:var(--amber)} .dr{background:var(--red)}
/* ── PROGRESS ── */
.pgbar{background:var(--bg2);border-bottom:1px solid var(--brd);padding:10px 32px;display:flex;align-items:center;gap:16px}
.pg-lbl{font-size:10px;letter-spacing:1px;text-transform:uppercase;color:var(--t3);white-space:nowrap;font-weight:500}
.pg-track{flex:1;height:4px;background:var(--s3);border-radius:2px;overflow:hidden}
.pg-fill{height:100%;background:linear-gradient(90deg,var(--green3),var(--green));border-radius:2px;transition:width .7s cubic-bezier(.4,0,.2,1)}
.pg-pct{font-family:var(--disp);font-weight:600;color:var(--green);font-size:14px;min-width:36px;text-align:right}
/* ── TABS ── */
.tabs{display:flex;padding:0 32px;border-bottom:1px solid var(--brd);background:var(--bg2);overflow-x:auto;gap:0}
.tabs::-webkit-scrollbar{height:0}
.tab{padding:13px 18px;font-size:12px;font-weight:400;color:var(--t3);cursor:pointer;border-bottom:2px solid transparent;transition:all .15s;display:flex;align-items:center;gap:6px;white-space:nowrap;user-select:none;margin-bottom:-1px}
.tab:hover{color:var(--t2)}
.tab.active{color:var(--text);border-bottom-color:var(--green);font-weight:500}
.tab-ico{font-size:13px;opacity:.8}
/* ── MAIN ── */
.main{padding:26px 32px;max-width:1600px;margin:0 auto}
.tab-content{display:none}
.tab-content.active{display:block}
/* ── PANEL HEADER ── */
.ph{display:flex;align-items:center;justify-content:space-between;margin-bottom:18px;flex-wrap:wrap;gap:10px}
.ph-title{font-family:var(--disp);font-size:17px;font-weight:600;color:var(--text);letter-spacing:-.2px}
.ph-sub{font-size:12px;color:var(--t2);margin-top:3px}
.fbar{display:flex;gap:6px;align-items:center;flex-wrap:wrap}
.fbtn{padding:6px 13px;border-radius:var(--rs);border:1px solid var(--brd2);background:transparent;color:var(--t2);font-family:var(--sans);font-size:12px;cursor:pointer;transition:all .15s}
.fbtn:hover{color:var(--text);background:var(--s2)}
.fbtn.active{border-color:rgba(61,220,132,.3);color:var(--green);background:var(--gdim)}
.srch{background:var(--s1);border:1px solid var(--brd2);border-radius:var(--rs);color:var(--text);font-family:var(--sans);font-size:13px;padding:6px 12px;outline:none;width:210px;transition:border-color .15s}
.srch:focus{border-color:rgba(61,220,132,.3)}
.srch::placeholder{color:var(--t3)}
/* ── TABLE ── */
.tbl-wrap{border:1px solid var(--brd);border-radius:var(--r);overflow:hidden;background:var(--s1)}
table{width:100%;border-collapse:collapse}
thead tr{background:var(--s2);border-bottom:1px solid var(--brd)}
th{padding:11px 16px;text-align:left;font-size:11px;letter-spacing:.5px;text-transform:uppercase;color:var(--t3);font-weight:500;white-space:nowrap}
tbody tr{border-bottom:1px solid var(--brd);transition:background .12s}
tbody tr:last-child{border-bottom:none}
tbody tr:hover{background:var(--s2)}
td{padding:14px 16px;vertical-align:middle}
.t-name{font-weight:500;font-size:14px;color:var(--text)}
.t-sub{font-size:12px;color:var(--t2);margin-top:3px;line-height:1.55}
.t-ico{font-size:16px;width:26px;flex-shrink:0;opacity:.85}
.t-row{display:flex;align-items:center;gap:9px}
/* ── BADGES ── */
.badge{display:inline-flex;align-items:center;padding:3px 9px;border-radius:4px;font-size:11px;font-weight:500;white-space:nowrap;letter-spacing:.2px}
.b-hld{background:var(--bdim);color:var(--blue);border:1px solid rgba(110,181,255,.15)}
.b-lld{background:var(--adim);color:var(--amber);border:1px solid rgba(245,166,35,.15)}
.b-cr{background:var(--pdim);color:var(--purple);border:1px solid rgba(167,139,250,.18)}
.b-st{background:var(--bdim);color:var(--blue);border:1px solid rgba(110,181,255,.15)}
.b-bh{background:var(--gdim);color:var(--green2);border:1px solid rgba(61,220,132,.15)}
.b-hb{background:var(--adim);color:var(--amber);border:1px solid rgba(245,166,35,.15)}
.b-lb{background:var(--rdim);color:var(--red);border:1px solid rgba(240,101,101,.15)}
.b-fund{background:var(--cdim);color:var(--cyan);border:1px solid rgba(34,211,238,.15)}
.diff-b{background:var(--gdim);color:var(--green2);border:1px solid rgba(61,220,132,.18)}
.diff-i{background:var(--adim);color:var(--amber);border:1px solid rgba(245,166,35,.15)}
.diff-a{background:var(--rdim);color:var(--red);border:1px solid rgba(240,101,101,.15)}
.imp-crit{background:var(--rdim);color:var(--red);border:1px solid rgba(240,101,101,.15)}
.imp-high{background:var(--adim);color:var(--amber);border:1px solid rgba(245,166,35,.15)}
.imp-med{background:var(--gdim);color:var(--green2);border:1px solid rgba(61,220,132,.15)}
.imp-low{background:var(--s3);color:var(--t2);border:1px solid var(--brd2)}
/* ── STATUS SELECT ── */
.ss{appearance:none;-webkit-appearance:none;border-radius:var(--rs);padding:6px 28px 6px 10px;font-family:var(--sans);font-size:12px;font-weight:400;cursor:pointer;outline:none;border:1px solid var(--brd2);background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='9' height='5' viewBox='0 0 9 5'%3E%3Cpath d='M0 0l4.5 5L9 0z' fill='%23444'/%3E%3C/svg%3E");background-repeat:no-repeat;background-position:right 8px center;transition:all .15s;min-width:132px}
.ss.ns{background-color:transparent;color:var(--t3)}
.ss.ac{background-color:var(--adim);color:var(--amber);border-color:rgba(245,166,35,.2)}
.ss.dn{background-color:var(--gdim);color:var(--green);border-color:rgba(61,220,132,.2)}
/* ── TAGS ── */
.tags{display:flex;flex-wrap:wrap;gap:5px}
.ctag{padding:3px 8px;border-radius:4px;font-size:10px;border:1px solid var(--brd2);color:var(--t3);background:transparent;white-space:nowrap}
/* ── LINK CHIPS ── */
.lchips{display:flex;flex-wrap:wrap;gap:5px;align-items:center}
.lchip{display:inline-flex;align-items:center;gap:4px;padding:4px 9px;border-radius:4px;font-size:11px;background:var(--bdim);border:1px solid rgba(110,181,255,.12);color:var(--blue);text-decoration:none;transition:all .15s;white-space:nowrap}
.lchip:hover{background:rgba(110,181,255,.13);border-color:rgba(110,181,255,.25)}
.add-lnk{display:inline-flex;align-items:center;gap:4px;padding:4px 9px;border-radius:4px;font-size:11px;background:transparent;border:1px dashed var(--brd2);color:var(--t3);cursor:pointer;transition:all .15s;font-family:var(--sans)}
.add-lnk:hover{border-color:rgba(61,220,132,.3);color:var(--green)}
/* ── RESOURCE CARDS (Library tab) ── */
.res-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(340px,1fr));gap:14px}
.res-card{background:var(--s1);border:1px solid var(--brd);border-radius:var(--r);padding:20px;transition:border-color .2s,box-shadow .2s;display:flex;flex-direction:column;gap:12px}
.res-card:hover{border-color:var(--brd2);box-shadow:0 4px 20px rgba(0,0,0,.3)}
.rc-top{display:flex;align-items:flex-start;justify-content:space-between;gap:8px}
.rc-title{font-weight:500;font-size:14px;color:var(--text);line-height:1.4}
.rc-author{font-size:12px;color:var(--t2);margin-top:3px}
.rc-desc{font-size:12px;color:var(--t2);line-height:1.7}
.rc-footer{display:flex;align-items:center;justify-content:space-between;flex-wrap:wrap;gap:6px;margin-top:2px}
.rc-tags{display:flex;gap:4px;flex-wrap:wrap}
.rc-link{display:inline-flex;align-items:center;gap:4px;padding:5px 14px;border-radius:4px;font-size:12px;background:var(--gdim);border:1px solid rgba(61,220,132,.2);color:var(--green);text-decoration:none;transition:all .15s;font-weight:500;white-space:nowrap}
.rc-link:hover{background:rgba(61,220,132,.12)}
.rc-free{font-size:10px;padding:2px 7px;border-radius:3px;background:var(--gdim);color:var(--green2);border:1px solid rgba(61,220,132,.15);font-weight:500}
.rc-paid{font-size:10px;padding:2px 7px;border-radius:3px;background:var(--adim);color:var(--amber);border:1px solid rgba(245,166,35,.15);font-weight:500}
/* ── SECTION DIVIDER ── */
.sdiv{display:flex;align-items:center;gap:12px;margin:22px 0 14px}
.sdiv-lbl{font-size:11px;letter-spacing:.8px;text-transform:uppercase;color:var(--t3);white-space:nowrap;font-weight:500}
.sdiv-line{flex:1;height:1px;background:var(--brd)}
/* ── QUESTION CARDS ── */
.q-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(400px,1fr));gap:12px}
.qcard{background:var(--s1);border:1px solid var(--brd);border-radius:var(--r);padding:20px;transition:border-color .2s}
.qcard:hover{border-color:var(--brd2)}
.qcard-top{display:flex;align-items:flex-start;gap:10px;margin-bottom:12px}
.qnum{font-size:10px;color:var(--t3);font-weight:500;letter-spacing:.5px;white-space:nowrap;margin-top:2px;min-width:30px}
.qtext{font-size:14px;color:var(--text);line-height:1.6;flex:1}
.fdots{display:flex;gap:3px;margin-top:3px}
.fd{width:6px;height:6px;border-radius:50%;background:var(--s3)}
.fd.on{background:var(--green);opacity:.9}
.qmeta{display:flex;gap:5px;flex-wrap:wrap}
.qtag{padding:3px 8px;border-radius:4px;font-size:11px}
.qt-topic{background:var(--gdim);color:var(--green2);border:1px solid rgba(61,220,132,.15)}
.qt-co{background:transparent;color:var(--t3);border:1px solid var(--brd2)}
.toggle-h{font-size:12px;color:var(--t3);cursor:pointer;background:none;border:none;font-family:var(--sans);padding:0;transition:color .15s;margin-top:12px;display:block}
.toggle-h:hover{color:var(--green)}
.hint-box{margin-top:10px;padding:13px 15px;background:var(--bg3);border-radius:var(--rs);border-left:2px solid rgba(61,220,132,.3);font-size:12px;color:var(--t2);line-height:1.8;display:none}
.hint-box.open{display:block}
/* ── ROADMAP ── */
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links:[
{t:"📹 Chat System (ByteByteGo)",u:"https://youtu.be/vvhC64hQZMk",lt:"video"},
{t:"📖 Designing WhatsApp",u:"https://www.geeksforgeeks.org/design-a-chat-system-like-whatsapp/",lt:"blog"},
]},
{ ico:"📸", name:"Instagram / Photo Feed",
desc:"Object storage, CDN, feed generation (push vs pull), follow graph.",
links:[
{t:"📹 Instagram (ByteByteGo)",u:"https://youtu.be/hnpzNAPiC0E",lt:"video"},
{t:"📖 Grokking — Instagram",u:"https://www.educative.io/courses/grokking-the-system-design-interview/m22LWKgXOEm",lt:"course"},
]},
{ ico:"🐦", name:"Twitter Timeline (Fanout)",
desc:"Fanout-on-write vs read. Celebrity problem. Redis timeline cache.",
links:[
{t:"📹 Twitter Design (Gaurav Sen)",u:"https://youtu.be/wYk0xPP_P_8",lt:"video"},
{t:"📖 Twitter Real Architecture",u:"https://blog.twitter.com/engineering/en_us/topics/infrastructure",lt:"blog"},
]},
{ ico:"🔔", name:"Notification System",
desc:"APNs, FCM, fanout queue, priority, retries, user preferences.",
links:[
{t:"📹 Notification System (ByteByteGo)",u:"https://youtu.be/bBTPZ9NdSk8",lt:"video"},
{t:"📖 Notification Design Guide",u:"https://www.geeksforgeeks.org/notification-system-design/",lt:"blog"},
]},
{ ico:"🅿️", name:"Parking Lot (LLD)",
desc:"Singleton, Strategy (pricing), multiple vehicle types, tickets, floors.",
links:[
{t:"📹 Parking Lot LLD (Udit Agarwal)",u:"https://youtu.be/DSGsa0pu8-k",lt:"video"},
{t:"📖 Parking Lot LLD Guide",u:"https://www.geeksforgeeks.org/design-parking-lot-using-ood/",lt:"blog"},
]},
{ ico:"💾", name:"LRU Cache (LLD)",
desc:"HashMap + Doubly linked list. O(1) get/put. Thread-safe variant.",
links:[
{t:"📹 LRU Cache (Nick White)",u:"https://youtu.be/S6IfqDXWa10",lt:"video"},
{t:"📖 LRU Cache Implementation",u:"https://www.geeksforgeeks.org/lru-cache-implementation/",lt:"blog"},
]},
]
},
{
phase:"Phase 5 — Advanced System Design", icon:"🚀", badge:"Advanced", badgeCls:"diff-a",
sub:"Distributed systems at scale. The problems that separate senior engineers.",
items:[
{ ico:"▶️", name:"Video Streaming (YouTube/Netflix)",
desc:"HLS/DASH, adaptive bitrate, transcoding pipeline, CDN strategy.",
links:[
{t:"📹 Netflix Architecture (InfoQ)",u:"https://youtu.be/psQzyFfsUGU",lt:"video"},
{t:"📖 Netflix Tech Blog",u:"https://netflixtechblog.com",lt:"blog"},
{t:"📖 Grokking — YouTube",u:"https://www.educative.io/courses/grokking-the-system-design-interview/xV26VjZ7yMl",lt:"course"},
]},
{ ico:"🚗", name:"Uber / Ride Sharing",
desc:"Geohash, driver matching, real-time location, surge pricing, ETA.",
links:[
{t:"📹 Uber Design (Gaurav Sen)",u:"https://youtu.be/umWABit-wbk",lt:"video"},
{t:"📖 Uber Engineering Blog",u:"https://eng.uber.com",lt:"blog"},
]},
{ ico:"📄", name:"Google Docs (Real-time Collab)",
desc:"Operational Transformation, CRDT, vector clocks, WebSocket broadcast.",
links:[
{t:"📹 Google Docs Architecture",u:"https://youtu.be/2auwirNBvGg",lt:"video"},
{t:"📖 OT & CRDT Explained",u:"https://www.geeksforgeeks.org/real-time-collaboration-tool-system-design/",lt:"blog"},
]},
{ ico:"💳", name:"Payment System",
desc:"Idempotency keys, double-spend prevention, saga pattern, distributed ledger.",
links:[
{t:"📹 Payment System Design",u:"https://youtu.be/olfaBgJrUBI",lt:"video"},
{t:"📖 Stripe Engineering Blog",u:"https://stripe.com/blog/engineering",lt:"blog"},
]},
{ ico:"🔍", name:"Search Engine (Google Search)",
desc:"Web crawler, inverted index, TF-IDF, PageRank, serving layer.",
links:[
{t:"📹 Search Engine Design (Gaurav Sen)",u:"https://youtu.be/0LTXCcVRQi0",lt:"video"},
{t:"📖 Google Research Papers",u:"https://research.google/pubs",lt:"blog"},
]},
{ ico:"📨", name:"Distributed Message Queue (Kafka)",
desc:"Partitions, consumer groups, log compaction, exactly-once semantics.",
links:[
{t:"📹 Kafka Architecture Deep Dive",u:"https://youtu.be/Ch5VhJzaoaI",lt:"video"},
{t:"📖 Kafka Definitive Guide (Free)",u:"https://www.confluent.io/resources/kafka-the-definitive-guide",lt:"blog"},
]},
{ ico:"💰", name:"Distributed Transactions",
desc:"2-Phase Commit, Saga pattern, compensating transactions, CQRS + Event Sourcing.",
links:[
{t:"📹 Distributed Transactions (Hussain Nasser)",u:"https://youtu.be/S4FnmSeRpAY",lt:"video"},
{t:"📖 Saga Pattern — microservices.io",u:"https://microservices.io/patterns/data/saga.html",lt:"blog"},
]},
]
},
{
phase:"Phase 6 — Distributed Systems Deep Dive", icon:"🌍", badge:"Advanced", badgeCls:"diff-a",
sub:"Internals of databases, consensus, and large-scale infrastructure.",
items:[
{ ico:"📖", name:"Designing Data-Intensive Applications",
desc:"The bible of distributed systems. Replication, partitioning, transactions, consensus.",
links:[
{t:"📹 DDIA Book Summary",u:"https://youtu.be/PdtlXdse7pw",lt:"video"},
{t:"📖 DDIA — Martin Kleppmann",u:"https://dataintensive.net",lt:"blog"},
{t:"📖 DDIA Notes (GitHub)",u:"https://github.com/donnemartin/system-design-primer",lt:"github"},
]},
{ ico:"🗳️", name:"Consensus: Raft & Paxos",
desc:"Leader election, log replication, split-brain prevention.",
links:[
{t:"📹 Raft Consensus (MIT 6.824)",u:"https://youtu.be/64Zp3tzNbpE",lt:"video"},
{t:"📖 The Raft Paper",u:"https://raft.github.io/raft.pdf",lt:"blog"},
{t:"🎮 Raft Visualization",u:"https://raft.github.io",lt:"blog"},
]},
{ ico:"🕰️", name:"Clocks & Ordering (Vector Clocks)",
desc:"Logical clocks, Lamport timestamps, vector clocks, causality.",
links:[
{t:"📹 Distributed Clocks (Martin Kleppmann)",u:"https://youtu.be/FQ_2N3AoinU",lt:"video"},
{t:"📖 Lamport Clock Paper",u:"https://lamport.azurewebsites.net/pubs/time-clocks.pdf",lt:"blog"},
]},
{ ico:"🏛️", name:"Storage Engines (LSM vs B-Tree)",
desc:"How RocksDB, Cassandra (LSM) vs MySQL, Postgres (B-Tree) work internally.",
links:[
{t:"📹 LSM Tree (Hussein Nasser)",u:"https://youtu.be/I6jB0nM9SKU",lt:"video"},
{t:"📖 DDIA Chapter 3",u:"https://dataintensive.net",lt:"blog"},
]},
]
},
];
// ─────────────────────────────────────────────────────────────
const HLD_TOPICS = [
{id:"h1", ico:"🔗", name:"URL Shortener", imp:"critical", cos:["Amazon","Google","Uber","Microsoft"],
desc:"Base62 encoding, KV store for redirects, analytics, custom aliases, expiry",
links:[{t:"ByteByteGo Video",u:"https://youtu.be/JQDHz72LtRQ"},{t:"Grokking TinyURL",u:"https://www.educative.io/courses/grokking-the-system-design-interview/m2ygV4E81AR"}]},
{id:"h2", ico:"🐦", name:"Twitter / Social Feed", imp:"critical", cos:["Twitter","Meta","LinkedIn","Snap"],
desc:"Fanout on write vs read, celebrity problem, Redis sorted sets for timeline",
links:[{t:"ByteByteGo Video",u:"https://youtu.be/wYk0xPP_P_8"},{t:"Grokking Twitter",u:"https://www.educative.io/courses/grokking-the-system-design-interview/m2G48X18NDO"}]},
{id:"h3", ico:"▶️", name:"YouTube / Video Streaming", imp:"critical", cos:["Netflix","YouTube","Amazon","Disney+"],
desc:"HLS/DASH adaptive bitrate, transcoding pipeline, CDN edge delivery, S3 storage",
links:[{t:"Netflix Architecture",u:"https://youtu.be/psQzyFfsUGU"},{t:"Grokking YouTube",u:"https://www.educative.io/courses/grokking-the-system-design-interview/xV26VjZ7yMl"}]},
{id:"h4", ico:"💬", name:"WhatsApp / Chat System", imp:"critical", cos:["WhatsApp","Slack","Discord","Telegram"],
desc:"WebSocket, offline delivery, message ordering, E2E encryption, Cassandra",
links:[{t:"ByteByteGo Chat",u:"https://youtu.be/vvhC64hQZMk"},{t:"Designing WhatsApp",u:"https://www.geeksforgeeks.org/design-a-chat-system-like-whatsapp/"}]},
{id:"h5", ico:"🚗", name:"Uber / Ride Sharing", imp:"critical", cos:["Uber","Lyft","Ola","DoorDash"],
desc:"Geohash geo-indexing, real-time driver location, ETA, matching, surge pricing",
links:[{t:"Gaurav Sen Video",u:"https://youtu.be/umWABit-wbk"},{t:"Uber Engineering Blog",u:"https://eng.uber.com"}]},
{id:"h6", ico:"🚦", name:"Rate Limiter", imp:"critical", cos:["Stripe","Cloudflare","Google","Amazon"],
desc:"Token bucket, sliding window log, sliding window counter, Redis + Lua atomic ops",
links:[{t:"ByteByteGo Rate Limiter",u:"https://youtu.be/FU4WlwfS3G0"},{t:"System Design Rate Limiter",u:"https://www.geeksforgeeks.org/rate-limiting-in-system-design/"}]},
{id:"h7", ico:"⚡", name:"Distributed Cache (Redis)", imp:"critical", cos:["Amazon","Google","Meta","Netflix"],
desc:"Eviction (LRU/LFU), consistent hashing for cache nodes, write policies, hot keys",
links:[{t:"Redis Architecture",u:"https://youtu.be/OqCK95AS-YE"},{t:"Distributed Cache Design",u:"https://www.geeksforgeeks.org/design-a-key-value-store-using-distributed-cache/"}]},
{id:"h8", ico:"📨", name:"Message Queue (Kafka)", imp:"critical", cos:["LinkedIn","Uber","Netflix","Airbnb"],
desc:"Partitions, consumer groups, log compaction, at-least-once vs exactly-once",
links:[{t:"Kafka Deep Dive",u:"https://youtu.be/Ch5VhJzaoaI"},{t:"Kafka Definitive Guide",u:"https://www.confluent.io/resources/kafka-the-definitive-guide"}]},
{id:"h9", ico:"🔄", name:"Consistent Hashing", imp:"critical", cos:["Amazon","Google","Cassandra","Redis"],
desc:"Hash ring, virtual nodes, minimal data movement on add/remove server",
links:[{t:"ByteByteGo Consistent Hashing",u:"https://youtu.be/UF9WA4k-iDM"},{t:"Consistent Hashing Explained",u:"https://www.geeksforgeeks.org/consistent-hashing/"}]},
{id:"h10",ico:"📐", name:"CAP Theorem / BASE / ACID", imp:"critical", cos:["All FAANG","Stripe","Cloudflare"],
desc:"C/A/P tradeoffs, CP vs AP systems, eventual consistency, MongoDB vs Cassandra",
links:[{t:"CAP Theorem (ByteByteGo)",u:"https://youtu.be/BHqjEjzAicA"},{t:"CAP FAQ",u:"https://www.cl.cam.ac.uk/research/dtg/archived/files/publications/public/mk428/cap-critique.pdf"}]},
{id:"h11",ico:"🗃️", name:"Database Sharding", imp:"critical", cos:["Amazon","Uber","Airbnb","Pinterest"],
desc:"Range vs hash sharding, hot spots, cross-shard queries, resharding strategy",
links:[{t:"Sharding (ByteByteGo)",u:"https://youtu.be/5faMjKuB9bc"},{t:"Database Sharding Guide",u:"https://www.geeksforgeeks.org/database-sharding-a-system-design-concept/"}]},
{id:"h12",ico:"🔀", name:"API Gateway / Load Balancer", imp:"critical", cos:["Amazon","Netflix","Uber","Cloudflare"],
desc:"L4 vs L7 LB, round-robin, least connections, health checks, reverse proxy",
links:[{t:"Load Balancing (ByteByteGo)",u:"https://youtu.be/K0Ta65OqQkY"},{t:"API Gateway Design",u:"https://www.geeksforgeeks.org/what-is-api-gateway-system-design/"}]},
{id:"h13",ico:"📸", name:"Instagram / Photo Sharing", imp:"high", cos:["Meta","Pinterest","Snap","Twitter"],
desc:"Object storage (S3), CDN for images, feed generation, follow graph sharding",
links:[{t:"Instagram Architecture",u:"https://youtu.be/hnpzNAPiC0E"},{t:"Grokking Instagram",u:"https://www.educative.io/courses/grokking-the-system-design-interview/m22LWKgXOEm"}]},
{id:"h14",ico:"🛒", name:"Amazon / E-Commerce", imp:"high", cos:["Amazon","Flipkart","Shopify","eBay"],
desc:"Product catalog, inventory, cart, order service, payment, search",
links:[{t:"E-Commerce Design",u:"https://youtu.be/EpASu_1dUdE"},{t:"Amazon Architecture Blog",u:"https://www.allthingsdistributed.com"}]},
{id:"h15",ico:"🔔", name:"Notification System", imp:"high", cos:["Apple","Google","Meta","Slack"],
desc:"APNs/FCM gateways, priority queues, user preferences, retry, fan-out",
links:[{t:"Notification System (ByteByteGo)",u:"https://youtu.be/bBTPZ9NdSk8"},{t:"Notification Design",u:"https://www.geeksforgeeks.org/notification-system-design/"}]},
{id:"h16",ico:"📍", name:"Google Maps / Location", imp:"high", cos:["Google","Uber","DoorDash","Lyft"],
desc:"Geohash / S2 cells, routing algorithms, ETA prediction, map tiles",
links:[{t:"Google Maps Design",u:"https://youtu.be/jk3yvVfNvds"},{t:"Geospatial Indexing",u:"https://www.geeksforgeeks.org/design-google-maps/"}]},
{id:"h17",ico:"🗄️", name:"Distributed File Storage (S3)", imp:"high", cos:["Amazon","Google","Dropbox","Box"],
desc:"Object storage, chunking, erasure coding, deduplication, eventual consistency",
links:[{t:"Dropbox Design (Gaurav Sen)",u:"https://youtu.be/U0xTu6E2CT8"},{t:"Grokking Dropbox",u:"https://www.educative.io/courses/grokking-the-system-design-interview/gxMDOe16mql"}]},
{id:"h18",ico:"✏️", name:"Search Autocomplete", imp:"high", cos:["Google","Amazon","Twitter","LinkedIn"],
desc:"Trie, top-k suggestions per prefix, Kafka for frequency, Redis sorted sets",
links:[{t:"Typeahead (ByteByteGo)",u:"https://youtu.be/9jFpzpLHFcA"},{t:"Grokking Typeahead",u:"https://www.educative.io/courses/grokking-the-system-design-interview/mE2XkgGRnmp"}]},
{id:"h19",ico:"🎟️", name:"Ticketmaster / Event Booking", imp:"high", cos:["Ticketmaster","BookMyShow","Amazon"],
desc:"Seat reservation, concurrency with locks, payment, waiting room queue",
links:[{t:"Ticketmaster Design",u:"https://youtu.be/lBAwJgoO3Ek"},{t:"Ticketmaster LLD",u:"https://www.geeksforgeeks.org/design-a-system-like-bookmyshow/"}]},
{id:"h20",ico:"📄", name:"Google Docs / Collaborative Editor", imp:"high", cos:["Google","Microsoft","Notion","Atlassian"],
desc:"Operational Transformation or CRDT, real-time sync, conflict resolution",
links:[{t:"Google Docs Architecture",u:"https://youtu.be/2auwirNBvGg"},{t:"OT & CRDT Deep Dive",u:"https://www.geeksforgeeks.org/real-time-collaboration-tool-system-design/"}]},
{id:"h21",ico:"💳", name:"Payment System", imp:"high", cos:["Stripe","PayPal","Razorpay","Square"],
desc:"Idempotency keys, ledger design, saga pattern for rollbacks, PCI-DSS",
links:[{t:"Payment System Design",u:"https://youtu.be/olfaBgJrUBI"},{t:"Stripe Engineering Blog",u:"https://stripe.com/blog/engineering"}]},
{id:"h22",ico:"🆔", name:"Distributed ID Generator", imp:"high", cos:["Twitter","Instagram","Uber","Discord"],
desc:"Snowflake ID, UUID v4/v7, sonyflake, monotonic IDs, clock skew",
links:[{t:"Unique ID (ByteByteGo)",u:"https://youtu.be/lfhGHm2DcME"},{t:"Twitter Snowflake",u:"https://blog.twitter.com/engineering/en_us/a/2010/announcing-snowflake"}]},
{id:"h23",ico:"⚠️", name:"Circuit Breaker / Resiliency", imp:"high", cos:["Netflix","Amazon","Uber","Microsoft"],
desc:"Hystrix, retry with backoff, bulkhead, timeout, fallback patterns",
links:[{t:"Circuit Breaker Pattern",u:"https://youtu.be/ADHjZe4JZp4"},{t:"Netflix Hystrix",u:"https://github.com/Netflix/Hystrix/wiki"}]},
{id:"h24",ico:"🌐", name:"CDN", imp:"high", cos:["Cloudflare","Amazon","Netflix","Akamai"],
desc:"Push vs pull CDN, edge PoPs, cache invalidation, origin shield",
links:[{t:"CDN (Fireship)",u:"https://youtu.be/RI9np1LWzqw"},{t:"How CDN Works",u:"https://www.cloudflare.com/learning/cdn/what-is-a-cdn"}]},
{id:"h25",ico:"🎯", name:"Recommendation Engine", imp:"medium", cos:["Netflix","Spotify","Amazon","YouTube"],
desc:"Collaborative filtering, content-based, matrix factorization, feature pipeline",
links:[{t:"Recommendation System",u:"https://youtu.be/n3RKsY2H-NE"},{t:"Netflix Personalization",u:"https://netflixtechblog.com/system-architectures-for-personalization-and-recommendation-e081aa94b5d8"}]},
{id:"h26",ico:"🕷️", name:"Web Crawler", imp:"medium", cos:["Google","Amazon","Bing"],
desc:"BFS/DFS traversal, politeness, deduplication with Bloom filter, URL frontier",
links:[{t:"Web Crawler (ByteByteGo)",u:"https://youtu.be/BKZxZwUgL3Y"},{t:"Grokking Web Crawler",u:"https://www.educative.io/courses/grokking-the-system-design-interview/NE5LpPrWrKv"}]},
{id:"h27",ico:"📈", name:"Metrics & Logging System", imp:"medium", cos:["Datadog","Splunk","Netflix","Uber"],
desc:"Time-series DB, aggregation pipeline, alerting, distributed tracing (Jaeger)",
links:[{t:"Metrics System Design",u:"https://youtu.be/kIcq1_pBQSY"},{t:"Distributed Logging",u:"https://www.geeksforgeeks.org/distributed-logging-system-design/"}]},
{id:"h28",ico:"💱", name:"Distributed Transactions (Saga/2PC)", imp:"high", cos:["Amazon","Stripe","Airbnb"],
desc:"Two-phase commit, saga choreography vs orchestration, compensating transactions",
links:[{t:"Distributed Transactions",u:"https://youtu.be/S4FnmSeRpAY"},{t:"Saga Pattern",u:"https://microservices.io/patterns/data/saga.html"}]},
];
const LLD_TOPICS = [
{id:"l1", ico:"💾", name:"LRU Cache", imp:"critical", cos:["Google","Amazon","Meta","Microsoft"],
desc:"HashMap + DLL, O(1) get/put, eviction, thread-safe variant",
links:[{t:"Nick White LRU Video",u:"https://youtu.be/S6IfqDXWa10"},{t:"LRU Implementation",u:"https://www.geeksforgeeks.org/lru-cache-implementation/"}]},
{id:"l2", ico:"🔩", name:"SOLID Principles", imp:"critical", cos:["All FAANG","Atlassian","Microsoft"],
desc:"SRP, OCP, LSP, ISP, DIP — with real-world code examples",
links:[{t:"SOLID (ArjanCodes)",u:"https://youtu.be/pTB0EiLXUC8"},{t:"SOLID — DigitalOcean",u:"https://www.digitalocean.com/community/conceptual-articles/s-o-l-i-d-the-first-five-principles-of-object-oriented-design"}]},
{id:"l3", ico:"🏭", name:"Design Patterns (GoF)", imp:"critical", cos:["All FAANG","Salesforce","Atlassian"],
desc:"All 23 Gang of Four patterns — creational, structural, behavioural",
links:[{t:"Refactoring.Guru",u:"https://refactoring.guru/design-patterns"},{t:"Christopher Okhravi (YouTube)",u:"https://youtube.com/playlist?list=PLrhzvIcii6GNjpARjnq4yD3HHUnTSN5pC"}]},
{id:"l4", ico:"🅿️", name:"Parking Lot System", imp:"high", cos:["Amazon","Microsoft","Uber"],
desc:"Singleton, Strategy (pricing), multiple vehicle types, tickets, floors",
links:[{t:"Parking Lot Video",u:"https://youtu.be/DSGsa0pu8-k"},{t:"Parking Lot Guide",u:"https://www.geeksforgeeks.org/design-parking-lot-using-ood/"}]},
{id:"l5", ico:"🛗", name:"Elevator System", imp:"high", cos:["Amazon","Google","Microsoft"],
desc:"SCAN algorithm, State machine (IDLE/UP/DOWN), request scheduling",
links:[{t:"Elevator LLD Video",u:"https://youtu.be/siqiJAJWUVA"},{t:"Elevator LLD Guide",u:"https://www.geeksforgeeks.org/design-elevator-system/"}]},
{id:"l6", ico:"🏧", name:"ATM System", imp:"high", cos:["Amazon","Google","IBM"],
desc:"State machine (Idle→Card→Pin→Amount→Dispense), card, account, transactions",
links:[{t:"ATM LLD Video",u:"https://youtu.be/vJkDzFnRJr4"},{t:"ATM LLD Guide",u:"https://www.geeksforgeeks.org/low-level-design-atm-machine/"}]},
{id:"l7", ico:"🥤", name:"Vending Machine", imp:"high", cos:["Amazon","Google","Uber"],
desc:"State pattern, inventory management, payment processing, change dispensing",
links:[{t:"Vending Machine Video",u:"https://youtu.be/DCCo8mDkMoU"},{t:"Vending Machine Guide",u:"https://www.geeksforgeeks.org/design-a-vending-machine/"}]},
{id:"l8", ico:"♟️", name:"Chess / Board Game", imp:"high", cos:["Amazon","Google","Microsoft"],
desc:"Polymorphic pieces, move validation, check/checkmate detection, game state",
links:[{t:"Chess LLD Video",u:"https://youtu.be/3HHivbOHMDs"},{t:"Chess LLD Guide",u:"https://www.geeksforgeeks.org/design-a-chess-game/"}]},
{id:"l9", ico:"💰", name:"Splitwise", imp:"high", cos:["Airbnb","Uber","Amazon"],
desc:"Group expenses, equal/exact/percentage splits, debt simplification algorithm",
links:[{t:"Splitwise Video",u:"https://youtu.be/rMnf-rA_FpM"},{t:"Splitwise LLD Guide",u:"https://www.geeksforgeeks.org/low-level-design-of-expense-sharing-app-like-splitwise/"}]},
{id:"l10",ico:"🎬", name:"Movie Ticket Booking", imp:"high", cos:["BookMyShow","Ticketmaster","Fandango"],
desc:"Theatre/show/seat hierarchy, concurrent seat locking, payment, optimistic locking",
links:[{t:"BookMyShow Video",u:"https://youtu.be/lBAwJgoO3Ek"},{t:"BookMyShow LLD",u:"https://www.geeksforgeeks.org/design-bookmyshow-a-system-design-interview-question/"}]},
{id:"l11",ico:"🏨", name:"Hotel Booking", imp:"high", cos:["Booking.com","Airbnb","Expedia"],
desc:"Room availability, date range queries, concurrent booking, strategy pricing",
links:[{t:"Hotel Booking Video",u:"https://youtu.be/hJPjADJ1_JM"},{t:"Hotel Booking LLD",u:"https://www.geeksforgeeks.org/design-a-hotel-booking-system-like-oyo-system-design/"}]},
{id:"l12",ico:"🍕", name:"Food Delivery (Swiggy/Zomato)", imp:"high", cos:["Swiggy","Zomato","DoorDash","Uber Eats"],
desc:"Restaurant, menu, cart, order lifecycle, delivery agent assignment",
links:[{t:"Food Delivery LLD",u:"https://youtu.be/iJLD4TAIvpM"},{t:"Food Delivery Guide",u:"https://www.geeksforgeeks.org/design-food-ordering-system-like-swiggy/"}]},
{id:"l13",ico:"👁️", name:"Observer Pattern", imp:"critical", cos:["All FAANG","Salesforce","SAP"],
desc:"Subject notifies observers, event bus, decoupled pub-sub in-process",
links:[{t:"Observer (Christopher Okhravi)",u:"https://youtu.be/_BpmfnqjgzQ"},{t:"Observer — Refactoring.Guru",u:"https://refactoring.guru/design-patterns/observer"}]},
{id:"l14",ico:"♟️", name:"Strategy Pattern", imp:"critical", cos:["All FAANG","Stripe","Atlassian"],
desc:"Swap algorithms at runtime, payment strategies, sorting strategies",
links:[{t:"Strategy (Christopher Okhravi)",u:"https://youtu.be/v9ejT8FO-7I"},{t:"Strategy — Refactoring.Guru",u:"https://refactoring.guru/design-patterns/strategy"}]},
{id:"l15",ico:"🔄", name:"State Pattern", imp:"critical", cos:["Amazon","Google","Microsoft"],
desc:"Object behaviour changes with state, FSM, vending machine, ATM, order lifecycle",
links:[{t:"State (Christopher Okhravi)",u:"https://youtu.be/N12L5D78MAA"},{t:"State — Refactoring.Guru",u:"https://refactoring.guru/design-patterns/state"}]},
{id:"l16",ico:"🧵", name:"Concurrency & Thread Safety", imp:"high", cos:["All FAANG","Microsoft"],
desc:"Race conditions, deadlocks, mutex, semaphore, ReentrantLock, ThreadLocal",
links:[{t:"Java Concurrency (Amigoscode)",u:"https://youtu.be/d9s_d28yJq0"},{t:"JCIP Book",u:"https://jcip.net"}]},
{id:"l17",ico:"📋", name:"Library Management System", imp:"medium", cos:["Amazon","Google","Microsoft"],
desc:"Books, members, lending, fines, reservations, search by author/ISBN",
links:[{t:"Library LLD Video",u:"https://youtu.be/q6CjxMQE5_Q"},{t:"Library LLD Guide",u:"https://www.geeksforgeeks.org/design-library-management-system/"}]},
{id:"l18",ico:"🏏", name:"Cricinfo / Live Score", imp:"medium", cos:["Amazon","Google","ESPN"],
desc:"Match, innings, over, players, live updates, scorecard, commentary",
links:[{t:"Cricket LLD Video",u:"https://youtu.be/6PEE4zDRnUI"},{t:"Cricket LLD Guide",u:"https://www.geeksforgeeks.org/design-cricinfo-for-live-matches/"}]},
];
const PATTERNS = [
// ── FUNDAMENTALS ─────────────────────────────────────────────────────────
{id:"f1",ico:"🏗️",name:"OOP — 4 Pillars", cat:"Fundamentals",imp:"critical",
idea:"Encapsulation, Abstraction, Inheritance, Polymorphism. Foundation of every LLD interview.",
links:[
{t:"📹 OOP in 7 min (Fireship)", u:"https://youtu.be/pTB0EiLXUC8"},
{t:"📹 OOP Full Course (Programming w/ Mosh)",u:"https://youtu.be/GhctmPNv2go"},
{t:"📖 Baeldung — OOP Concepts", u:"https://www.baeldung.com/java-oop"},
{t:"📖 GeeksForGeeks OOP Primer", u:"https://www.geeksforgeeks.org/object-oriented-programming-oops-concept-in-java/"},
]},
{id:"f2",ico:"🔩",name:"SOLID Principles", cat:"Fundamentals",imp:"critical",
idea:"SRP, OCP, LSP, ISP, DIP. 5 rules for clean, maintainable, extensible OOP code.",
links:[
{t:"📹 SOLID in 12 min (ArjanCodes)", u:"https://youtu.be/pTB0EiLXUC8"},
{t:"📹 SOLID Deep Dive (Amigoscode)", u:"https://youtu.be/rtmFCcjEgEw"},
{t:"📖 DigitalOcean SOLID Guide", u:"https://www.digitalocean.com/community/conceptual-articles/s-o-l-i-d-the-first-five-principles-of-object-oriented-design"},
{t:"📖 Baeldung SOLID", u:"https://www.baeldung.com/solid-principles"},
{t:"📖 Refactoring.Guru SOLID", u:"https://refactoring.guru/refactoring/what-is-refactoring"},
]},
{id:"f3",ico:"🧩",name:"Composition over Inheritance", cat:"Fundamentals",imp:"high",
idea:"Prefer has-a over is-a. More flexible. Avoids brittle deep class hierarchies.",
links:[
{t:"📹 Composition vs Inheritance (Web Dev Simplified)",u:"https://youtu.be/wfMtDGfHWpA"},
{t:"📖 Head First Design Patterns — Ch.1", u:"https://www.oreilly.com/library/view/head-first-design/0596007124"},
{t:"📖 Medium — Composition over Inheritance",u:"https://www.geeksforgeeks.org/composition-vs-inheritance/"},
]},
{id:"f4",ico:"📐",name:"UML Class Diagrams", cat:"Fundamentals",imp:"high",
idea:"Draw classes, interfaces, and relationships before writing a single line of code.",
links:[
{t:"📹 UML Class Diagrams (Lucidchart)", u:"https://youtu.be/UI6lqHOVHic"},
{t:"📹 UML in 10 min (Derek Banas)", u:"https://youtu.be/OkC7HKtiZC0"},
{t:"📖 Visual Paradigm — UML Tutorial", u:"https://www.visual-paradigm.com/guide/uml-unified-modeling-language/uml-class-diagram-tutorial"},
{t:"📖 IBM — UML Basics", u:"https://developer.ibm.com/articles/the-class-diagram"},
]},
{id:"f5",ico:"🔀",name:"Interfaces vs Abstract Classes", cat:"Fundamentals",imp:"critical",
idea:"Interface = contract, supports multiple. Abstract = partial implementation. Know when to use each.",
links:[
{t:"📹 Interface vs Abstract (Telusko)", u:"https://youtu.be/7tS4ql6GQWI"},
{t:"📖 Baeldung — Interface vs Abstract", u:"https://www.baeldung.com/java-interface-vs-abstract-class"},
{t:"📖 GeeksForGeeks Deep Dive", u:"https://www.geeksforgeeks.org/difference-between-abstract-class-and-interface-in-java/"},
]},
{id:"f6",ico:"⚙️",name:"Concurrency & Thread Safety", cat:"Fundamentals",imp:"high",
idea:"Race conditions, deadlocks, mutex, semaphore, ReentrantLock, ThreadLocal, immutability.",
links:[
{t:"📹 Java Concurrency (Amigoscode)", u:"https://youtu.be/d9s_d28yJq0"},
{t:"📹 Concurrency in 20 min (Fireship)", u:"https://youtu.be/ZoqgAy3h4OM"},
{t:"📖 JCIP — Java Concurrency in Practice", u:"https://jcip.net"},
{t:"📖 Baeldung Concurrency Guide", u:"https://www.baeldung.com/java-concurrency"},
]},
// ── CREATIONAL ────────────────────────────────────────────────────────────
{id:"c1",ico:"1️⃣",name:"Singleton", cat:"Creational",imp:"critical",
idea:"One global instance. Thread-safe via enum or double-checked locking. Logger, Config, DB Pool.",
links:[
{t:"📹 Singleton (Christopher Okhravi)", u:"https://youtu.be/hUE_j6q0LTQ"},
{t:"📹 Singleton — All variants (Derek Banas)",u:"https://youtu.be/-KCxJVW2pC0"},
{t:"📖 Refactoring.Guru — Singleton", u:"https://refactoring.guru/design-patterns/singleton"},
{t:"📖 Baeldung — Java Singleton", u:"https://www.baeldung.com/java-singleton"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/singleton"},
]},
{id:"c2",ico:"🏭",name:"Factory Method", cat:"Creational",imp:"critical",
idea:"Let subclasses decide which object to create. Decouples instantiation from usage. Open/Closed.",
links:[
{t:"📹 Factory Method (Christopher Okhravi)",u:"https://youtu.be/EcFVTgRHJLM"},
{t:"📹 Factory in 5 min (Coding with John)", u:"https://youtu.be/EdFq_JIThqM"},
{t:"📖 Refactoring.Guru — Factory Method", u:"https://refactoring.guru/design-patterns/factory-method"},
{t:"📖 Baeldung — Factory Pattern", u:"https://www.baeldung.com/java-factory-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/factory-method"},
]},
{id:"c3",ico:"🏗️",name:"Abstract Factory", cat:"Creational",imp:"high",
idea:"Factory of factories. Create families of related objects. Cross-platform UI toolkit example.",
links:[
{t:"📹 Abstract Factory (Christopher Okhravi)",u:"https://youtu.be/v-GiuMmsXj4"},
{t:"📹 Abstract Factory (Derek Banas)", u:"https://youtu.be/MuCnHigB6qE"},
{t:"📖 Refactoring.Guru — Abstract Factory", u:"https://refactoring.guru/design-patterns/abstract-factory"},
{t:"📖 Baeldung — Abstract Factory", u:"https://www.baeldung.com/java-abstract-factory-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/abstract-factory"},
]},
{id:"c4",ico:"🔨",name:"Builder", cat:"Creational",imp:"critical",
idea:"Construct complex objects step by step. Fluent API. Avoids telescoping constructor anti-pattern.",
links:[
{t:"📹 Builder (Christopher Okhravi)", u:"https://youtu.be/M7Xi1yO_s8E"},
{t:"📹 Builder Pattern (Coding with John)", u:"https://youtu.be/to5qjafsfGQ"},
{t:"📖 Refactoring.Guru — Builder", u:"https://refactoring.guru/design-patterns/builder"},
{t:"📖 Baeldung — Builder Pattern", u:"https://www.baeldung.com/creational-design-patterns#builder"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/builder"},
]},
{id:"c5",ico:"🧬",name:"Prototype", cat:"Creational",imp:"medium",
idea:"Clone existing objects instead of constructing from scratch. Shallow vs deep copy.",
links:[
{t:"📹 Prototype (Derek Banas)", u:"https://youtu.be/AFbZhRL0Uz8"},
{t:"📹 Prototype Pattern (Aryan Programmer)", u:"https://youtu.be/DcFhITC9v0E"},
{t:"📖 Refactoring.Guru — Prototype", u:"https://refactoring.guru/design-patterns/prototype"},
{t:"📖 Baeldung — Prototype", u:"https://www.baeldung.com/java-pattern-prototype"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/prototype"},
]},
{id:"c6",ico:"🏊",name:"Object Pool", cat:"Creational",imp:"medium",
idea:"Reuse a fixed set of pre-created objects. Avoids expensive construction. DB connections, threads.",
links:[
{t:"📹 Object Pool Pattern (CodeVault)", u:"https://youtu.be/iKPXHY0GqSU"},
{t:"📖 Baeldung — Object Pool", u:"https://www.baeldung.com/java-object-pool-pattern"},
{t:"📖 Source Making — Object Pool", u:"https://sourcemaking.com/design_patterns/object_pool"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/object-pool"},
]},
// ── STRUCTURAL ────────────────────────────────────────────────────────────
{id:"s1",ico:"🔌",name:"Adapter", cat:"Structural",imp:"critical",
idea:"Convert an incompatible interface into the expected one. Wrap legacy or third-party classes.",
links:[
{t:"📹 Adapter (Christopher Okhravi)", u:"https://youtu.be/2PKQtcJjYvc"},
{t:"📹 Adapter in 5 min (Coding with John)", u:"https://youtu.be/wA3keqCeKtM"},
{t:"📖 Refactoring.Guru — Adapter", u:"https://refactoring.guru/design-patterns/adapter"},
{t:"📖 Baeldung — Adapter Pattern", u:"https://www.baeldung.com/java-adapter-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/adapter"},
]},
{id:"s2",ico:"🎁",name:"Decorator", cat:"Structural",imp:"critical",
idea:"Add responsibilities to objects dynamically. Wrap in decorator objects. Java I/O streams.",
links:[
{t:"📹 Decorator (Christopher Okhravi)", u:"https://youtu.be/GCraGHx6gso"},
{t:"📹 Decorator Pattern (Coding with John)", u:"https://youtu.be/v6tpISNjHf8"},
{t:"📖 Refactoring.Guru — Decorator", u:"https://refactoring.guru/design-patterns/decorator"},
{t:"📖 Baeldung — Decorator Pattern", u:"https://www.baeldung.com/java-decorator-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/decorator"},
]},
{id:"s3",ico:"🏠",name:"Facade", cat:"Structural",imp:"critical",
idea:"Provide a simple interface to a complex subsystem. Hide internal complexity from clients.",
links:[
{t:"📹 Facade (Christopher Okhravi)", u:"https://youtu.be/K4FkHVO5iac"},
{t:"📹 Facade Pattern (Derek Banas)", u:"https://youtu.be/B1Y8fcYrz5o"},
{t:"📖 Refactoring.Guru — Facade", u:"https://refactoring.guru/design-patterns/facade"},
{t:"📖 Baeldung — Facade Pattern", u:"https://www.baeldung.com/java-facade-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/facade"},
]},
{id:"s4",ico:"🪞",name:"Proxy", cat:"Structural",imp:"high",
idea:"Surrogate for another object. Lazy init, access control, logging, caching proxy.",
links:[
{t:"📹 Proxy (Christopher Okhravi)", u:"https://youtu.be/NwaabHqPwDI"},
{t:"📹 Proxy Pattern (Derek Banas)", u:"https://youtu.be/cHg5bWW4nUI"},
{t:"📖 Refactoring.Guru — Proxy", u:"https://refactoring.guru/design-patterns/proxy"},
{t:"📖 Baeldung — Proxy Pattern", u:"https://www.baeldung.com/java-proxy-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/proxy"},
]},
{id:"s5",ico:"🌳",name:"Composite", cat:"Structural",imp:"high",
idea:"Treat individual and composed objects uniformly. Tree structures. File system, UI component trees.",
links:[
{t:"📹 Composite (Christopher Okhravi)", u:"https://youtu.be/EWDmWbJ4wRA"},
{t:"📹 Composite Pattern (Derek Banas)", u:"https://youtu.be/2HUnoKyC9l0"},
{t:"📖 Refactoring.Guru — Composite", u:"https://refactoring.guru/design-patterns/composite"},
{t:"📖 Baeldung — Composite Pattern", u:"https://www.baeldung.com/java-composite-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/composite"},
]},
{id:"s6",ico:"🌉",name:"Bridge", cat:"Structural",imp:"medium",
idea:"Decouple abstraction from implementation. Both can vary independently. Cross-platform rendering.",
links:[
{t:"📹 Bridge (Christopher Okhravi)", u:"https://youtu.be/F1YQ7YRjttI"},
{t:"📹 Bridge Pattern (Derek Banas)", u:"https://youtu.be/9jIgSX2sDwg"},
{t:"📖 Refactoring.Guru — Bridge", u:"https://refactoring.guru/design-patterns/bridge"},
{t:"📖 Baeldung — Bridge Pattern", u:"https://www.baeldung.com/java-bridge-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/bridge"},
]},
{id:"s7",ico:"🪶",name:"Flyweight", cat:"Structural",imp:"medium",
idea:"Share fine-grained objects to save memory. Intrinsic (shared) vs extrinsic (per-use) state.",
links:[
{t:"📹 Flyweight (Christopher Okhravi)", u:"https://youtu.be/0vV-R2926ss"},
{t:"📹 Flyweight Pattern (Derek Banas)", u:"https://youtu.be/qscOsQV-K14"},
{t:"📖 Refactoring.Guru — Flyweight", u:"https://refactoring.guru/design-patterns/flyweight"},
{t:"📖 Baeldung — Flyweight", u:"https://www.baeldung.com/java-flyweight"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/flyweight"},
]},
// ── BEHAVIOURAL ───────────────────────────────────────────────────────────
{id:"b1",ico:"👁️",name:"Observer", cat:"Behavioural",imp:"critical",
idea:"Subject notifies subscribed observers when state changes. Foundation of event systems.",
links:[
{t:"📹 Observer (Christopher Okhravi)", u:"https://youtu.be/_BpmfnqjgzQ"},
{t:"📹 Observer Pattern (Coding with John)", u:"https://youtu.be/EacopFRKFtg"},
{t:"📖 Refactoring.Guru — Observer", u:"https://refactoring.guru/design-patterns/observer"},
{t:"📖 Baeldung — Observer Pattern", u:"https://www.baeldung.com/java-observer-pattern"},
{t:"💻 Code Example (GitHub)", u:"https://github.com/iluwatar/java-design-patterns/tree/master/observer"},
]},
{id:"b2",ico:"♟️",name:"Strategy", cat:"Behavioural",imp:"critical",
idea:"Define a family of algorithms, encapsulate each, make them interchangeable at runtime.",
links:[
{t:"📹 Strategy (Christopher Okhravi)", u:"https://youtu.be/v9ejT8FO-7I"},
{t:"📹 Strategy Pattern (Coding with John)", u:"https://youtu.be/Nrwj3gZiuJU"},
{t:"📖 Refactoring.Guru — Strategy", u:"https://refactoring.guru/design-patterns/strategy"},