Using Python or Java to answer leet code and other problems to prep for tech interviews
Last updated: April 18, 2026
~83 LeetCode problems covering arrays, hashmaps, two pointers, sliding window, linked lists, stacks, binary trees, graphs, dynamic programming, and more.
| # | Title | Solution | Time/Space Complexity | Methods/Notes | Date Completed |
|---|---|---|---|---|---|
| 1 | Two Sum | Python Java | O(N)/O(N) | Hashmap to see if seen the target num subtracted by current number -> return value if have | May 25, 2024 |
| 9 | Palindrome Number | Python | O(N)/O(1) | Convert to string and compare with two pointers | Sep 26, 2025 |
| 14 | Longest Common Prefix | Python Java | O(N)/O(M) for both | set empty string, iterate through all the strings at once (need 2 for loops), return when i == len(s) or s[i] != strs[0][i] | Apirl 04, 2024 |
| 20 | Valid Parentheses | Python | O(N)/O(N) | Stack, push matching close bracket, pop when match found | Feb 7, 2025 |
| 21 | Merge Two Sorted Lists | Java | O(N)/O(N) | Creating a new linked list and add in required order | June 5, 2024 |
| 26 | Remove Duplicates from Sorted Array | Python | O(N)/O(1) | Two pointers, swap unique values to front | Feb 23, 2025 |
| 27 | Remove Element | Python | O(N)/O(1) | Swap valid elements to front of array in-place | Feb 10, 2025 |
| 83 | Remove Duplicates from Sorted List | Python | O(N)/O(1) | Iterate through, skip duplicates by adjusting next pointers | Dec 16, 2025 |
| 88 | Merge Sorted Array | Python | O(N)/O(1) | Merge in reverse order, fill from end of nums1 | Feb 23, 2025 |
| 101 | Symmetric Tree | Python | O(N)/O(h) | Recursive mirror check comparing left.left with right.right | Feb 25, 2025 |
| 104 | Maximum Depth of Binary Tree | Python | O(N)/O(N) | DFS, return 1 + max depth of left and right subtrees | Feb 26, 2025 |
| 111 | Minimum Depth of Binary Tree | Python | O(N)/O(N) | DFS returning min depth of left and right subtrees | Dec 20, 2025 |
| 118 | Pascal's Triangle | Python Java | O(N^2)/O(N^2) | Dynamic Programming -> every row is a list/array itself -> recursive calling itself to use previous row to calculate current row | May 25, 2024 |
| 125 | Valid Palindrome | Java | O(N)/O(1) | Two pointers, start at each end and compare | June 1, 2024 |
| 169 | Majority Element | Python | M1: O(N)/O(N) M2: O(N)/O(1) |
M1: Hashmap freq count M2: Boyer-Moore voting algorithm |
Feb 23, 2025 |
| 203 | Remove Linked List Elements | Python | O(N)/O(1) | Dummy node + prev/curr pointers, skip matching nodes | Feb 24, 2025 |
| 206 | Reverse Linked List | Python Java | M1: O(N)/O(1) M2: O(N)/O(N) |
M1: Iteratively M2:Recursively | June 5, 2024 |
| 217 | Contains Duplicate | Python | M1: O(N^2)/O(1) M2: O(NlogN)/O(logN) M3: O(N)/O(N) |
M1: Brute Force M2: sort array first, compare adjacent elements M3: put elements into HashMap -> containsKey then return true, else false |
May 25, 2024 |
| 242 | Valid Anagram | Python | M1: O(N)/O(N) M2: O(NlogN)/O(1) but could also be said to be O(N) for space |
M1: using Hashmap to count number of each character M2: sort the string first |
May 26, 2024 |
| 268 | Missing Number | Python | O(N)/O(N) | Put nums in set, iterate 0 to n to find missing | Dec 15, 2025 |
| 270 | Closest Binary Search Tree Value | Python | O(logN)/O(logN) | DFS using BST property to go left/right based on target | Dec 20, 2025 |
| 283 | Move Zeroes | Python | O(N)/O(1) | Two pointers, swap non-zero values to front | Feb 23, 2025 |
| 344 | Reverse String | Python Java | O(N)/O(1) | Two pointers, start at each end and swap characters | Dec 14, 2025 |
| 346 | Moving Average from Data Stream | Python | O(1)/O(N) | Queue with running sum, pop oldest when exceeding size | Dec 17, 2025 |
| 349 | Intersection of Two Arrays | Python | O(N*M)/O(N) | Iterate shorter array, check if in longer and not in result | Mar 21, 2026 |
| 383 | Ransom Note | Python | O(N+M)/O(N+M) | Hashmap freq count for both strings, compare counts | Dec 16, 2025 |
| 409 | Longest Palindrome | Python | O(N)/O(1) | Set to track pairs, count matched pairs * 2, +1 if any remain | Feb 26, 2025 |
| 448 | Find All Numbers Disappeared in an Array | Python | O(N)/O(1) | Mark visited indices negative, remaining positives are missing | Mar 23, 2026 |
| 485 | Max Consecutive Ones | Python | O(N)/O(1) | Track last seen 0, calculate distance from it | Mar 23, 2026 |
| 496 | Next Greater Element I | Python | O(N+M)/O(N+M) | Monotonic stack to find next greater in nums2, hashmap for nums1 indices | Dec 19, 2025 |
| 543 | Diameter of Binary Tree | Python | O(N)/O(N) | DFS returning height, track max left+right at each node | Dec 20, 2025 |
| 557 | Reverse Words in a String III | Python | O(N)/O(N) | Two pointers to reverse each word individually | Dec 15, 2025 |
| 643 | Maximum Average Subarray I | Python | O(N)/O(1) | Fixed sliding window, maintain sum by adding/removing elements | Dec 15, 2025 |
| 645 | Set Mismatch | Python | O(N)/O(1) | Mark visited as negative, find duplicate (already negative) and missing (still positive) | Mar 23, 2026 |
| 671 | Second Minimum Node in a Binary Tree | Java | O(N)/O(N) | DFS -- preorder traversal but custom towards this special kind of tree -> think case by case | Apirl 23, 2024 |
| 746 | Min Cost Climbing Stairs | Java | O(N)/O(1) | DP -> base case first two steps -> loop curr = cost[i] + min(first,second), first = second, second = curr | Apirl 20, 2024 |
| 771 | Jewels and Stones | Python | O(N+M)/O(N+M) | Hashmap freq count for both, sum matching keys | Dec 16, 2025 |
| 876 | Middle of Linked List | Python Python | O(N)/O(1) | Slow/fast pointers | Dec 16, 2025 |
| 929 | Unique Email Addresses | Python | O(N)/O(N) | Set + character building, handle dots and plus in local name | Sep 27, 2025 |
| 977 | Squares of a Sorted Array | Python | O(N)/O(N) | Two pointers from both ends, fill result array from back | Dec 14, 2025 |
| 1071 | Greatest Common Divisor of Strings | Python | O(min(m,n)*(n+m))/O(1) | Try substrings from largest, check if it divides both strings | Feb 23, 2025 |
| 1133 | Largest Unique Number | Python | O(N)/O(N) | Hashmap freq count, find largest with count of 1 | Dec 16, 2025 |
| 1189 | Maximum Number of Balloons | Python | O(N)/O(1) | Count chars in "balloon", divide l and o by 2, return min | Dec 16, 2025 |
| 1200 | Minimum Absolute Difference | Python | O(NlogN)/O(N) | Sort array, find min diff, collect all pairs with that diff | Dec 23, 2025 |
| 1207 | Unique Number of Occurrences | Python | O(N)/O(N) | Hashmap freq count, check len(freq) == len(set of values) | Feb 23, 2025 |
| 1365 | How Many Numbers Are Smaller Than the Current Number | Python | O(NlogN)/O(N) | Hashmap freq count, sort keys, prefix sum of counts | Mar 23, 2026 |
| 1413 | Minimum Value to Get Positive Step by Step Sum | Python | O(N)/O(N) | Prefix sum, find minimum prefix and return its negation + 1 | Dec 15, 2025 |
| 1426 | Counting Elements | Python | O(N)/O(N) | Put all in set, count elements where element+1 exists | Dec 15, 2025 |
| 1431 | Kids with the Greatest Number of Candies | Python | O(N)/O(N) | Find max candy first, check each kid + extra >= max | Feb 23, 2025 |
| 1470 | Shuffle the Array | Python | O(N)/O(N) | Two pointers, left at start and right at middle, interleave | Mar 23, 2026 |
| 1480 | Running Sum of 1d Array | Python | O(N)/O(N) | Build prefix sum array | Dec 15, 2025 |
| 1544 | Make The String Great | Python | O(N)/O(N) | Stack, pop if top and current are same letter different case | Dec 17, 2025 |
| 1768 | Merge Strings Alternately | Python | O(N)/O(N) | Loop shorter string, add chars alternately, append remainder | Feb 7, 2025 |
| 1832 | Check if the Sentence Is Pangram | Python | O(N)/O(1) | Set of characters, check if length is 26 | Dec 15, 2025 |
| 1929 | Concatenation of Array | Python | O(N)/O(N) | Return nums + nums | Feb 24, 2026 |
| 1971 | Find if Path Exists in Graph | Python | O(V+E)/O(V+E) | Build adjacency list, DFS from source to destination | Dec 21, 2025 |
| # | Title | Solution | Time/Space Complexity | Methods/Notes | Date Completed |
|---|---|---|---|---|---|
| 3 | Longest Substring Without Repeating Characters | Python Python Java | O(N)/O(N) | Sliding window with hashmap or hashset to track seen chars | Dec 16, 2025 |
| 11 | Container With Most Water | Java | O(N)/O(1) | two pointers, starting at opposite ends, move smaller pointer after testing area | June 5, 2024 |
| 33 | Search in Rotated Sorted Array | Java | O(logN)/O(1) | binary search | June 5, 2024 |
| 49 | Group Anagrams | Python | O(N)/O(N)) | HashMap of charCount to the words that can make this anagram | May 31, 2024 |
| 56 | Merge Intervals | Python | O(NlogN)/O(N) | Sort by start, merge overlapping end values | Dec 23, 2025 |
| 71 | Simplify Path | Python | O(N)/O(N) | Stack, split by /, handle .. and . cases | Dec 17, 2025 |
| 92 | Reverse Linked List II | Python | O(N)/O(1) | Dummy node, iterate to left position, reverse sublist in-place | Dec 17, 2025 |
| 102 | Binary Tree Level Order Traversal | Python | O(N)/O(N) | BFS with queue, process nodes level by level | Feb 26, 2025 |
| 103 | Binary Tree Zigzag Level Order Traversal | Python | O(N)/O(N) | BFS level order, reverse odd levels | Dec 20, 2025 |
| 128 | Longest Consecutive Sequence | Python | O(N)/O(N) | Set + find sequence starts (no left neighbor), count length | Feb 7, 2025 |
| 143 | Reorder List | Java | O(N)/O(N) | two pointers, one at each end but with linked lists | June 5, 2024 |
| 151 | Reverse Words in a String | Python | O(N)/O(N) | Strip spaces, deque to push words in reverse order | Feb 23, 2025 |
| 155 | Min Stack | Java | O(1)/O(N) | Two stacks, main stack + auxiliary min stack | Feb 26, 2025 |
| 300 | Longest Increasing Subsequence | Python | O(N^2)/O(N) | DP, track LIS length at each index from right to left | Dec 23, 2025 |
| 323 | Number of Connected Components in an Undirected Graph | Python | O(V+E)/O(V+E) | Build adjacency list, DFS to count connected components | Dec 21, 2025 |
| 347 | Top K Frequent Elements | Python | M1: O(N)/O(N) M2: O(NlogK)/O(N) |
M1: Bucket Sort + HashMap and then loop through for highest frequencies M2: Heap/PQ that sort by freq of each quarter, output first k elements |
May 31, 2024 Feb 24, 2025 |
| 438 | Find All Anagrams in a String | Python | O(N)/O(N) | Fixed sliding window with Counter, compare window to target | Sep 3, 2025 |
| 525 | Contiguous Array | Python | O(N)/O(N) | Hashmap tracking first index of zeros-ones difference | Dec 16, 2025 |
| 560 | Subarray Sum Equals k | Python | O(N)/O(N) | Prefix sum hashmap, count freq of (currSum - k) | Feb 22, 2025 |
| 567 | Permutation in String | Python | O(N)/O(N) | Fixed sliding window with Counter, compare window to target | Sep 3, 2025 |
| 622 | Design Circular Queue | Java | O(1)/O(N) | Array with front/rear pointers, circular increment with modulo | Feb 26, 2025 |
| 695 | Max Area of Island | Python | O(MN)/O(MN) | DFS on each unvisited land cell, track max area | Dec 22, 2025 |
| 701 | Insert into a Binary Search Tree | Python | O(logN)/O(logN) | DFS using BST property, insert at null leaf position | Dec 20, 2025 |
| 743 | Network Delay Time | Python | O(NLogN)/O(N) O(E*logV) in terms of edges & vertex) |
Dikjstra's Algorithm using MinHeap + stack to visit all nodes and see shortest path/weight | May 20, 2024 |
| 901 | Online Stock Span | Python | O(N)/O(N) | Monotonic stack storing [price, span] pairs | Dec 20, 2025 |
| 912 | Sort an Array | Java | O(NLogN)/O(logN) | merge sort | May 20, 2024 |
| 994 | Rotting Oranges | Python | O(N^2)/O(N) | Simulation, update grid state round by round | Apr 8, 2026 |
| 1004 | Max Consecutive Ones III | Python | O(N)/O(1) | Sliding window, track zero count, shrink when > k | Dec 15, 2025 |
| 1026 | Maximum Difference Between Node and Ancestor | Python | O(N)/O(N) | DFS passing max and min ancestor values down | Dec 20, 2025 |
| 1302 | Deepest Leaves Sum | Python | O(N)/O(N) | BFS tracking depth, sum values at deepest level | Dec 20, 2025 |
| 1657 | Determine if Two Strings Are Close | Python | O(N)/O(1) | Hashmap freq, check same unique chars and matching freq distribution | Feb 23, 2025 |
| 2090 | K Radius Subarray Averages | Python | O(N)/O(N) | Prefix sum, calculate average for valid indices | Dec 15, 2025 |
| 2095 | Delete the Middle Node of a Linked List | Python | O(N)/O(1) | Slow/fast pointers, delete node at slow position | Feb 24, 2025 |
| 2225 | Find Players With Zero or One Losses | Python | O(NlogN)/O(N) | Hashmap loss count, separate into zero-loss and one-loss lists | Dec 16, 2025 |
| 2559 | Count Vowel Strings in Ranges | Python | O(N+Q)/O(N+Q) | Prefix sum of vowel-starting-and-ending strings | Dec 23, 2025 |
| # | Title | Solution | Time/Space Complexity | Methods/Notes | Date Completed |
|---|---|---|---|---|---|
| 32 | Longest Valid Parentheses | Python | O(N)/O(N) | Stack storing indices, track last valid position | Mar 4, 2025 |
| 76 | Minimum Window Substring | Python Python | O(N)/O(N) | Sliding window with Counter hashmaps, shrink when all conditions are met | Sep 3, 2025 |
| 295 | Find Median from Data Stream | Python | O(logN)/O(N) | Two heaps (max + min), maintain balanced sizes for O(1) median | Dec 23, 2025 |
| 2781 | Length of the Longest Valid Substring | Java | O(N * maxlengthofforbidden^2)/O(sum of forbidden words length) | Sliding Window + brute Force | June 1, 2024 |
| Name | Solution | Time/Space Complexity | Methods/Notes | Date Completed |
|---|---|---|---|---|
| UW Programming Competition 2024 -- N. Numerology | File Python |
