update 853 java

Author: yennanliu

README.md

@@ -455,7 +455,7 @@
 735| [Asteroid Collision](https://leetcode.com/problems/asteroid-collision/) | [Python](./leetcode_python/Stack/asteroid-collision.py)  | _O(n)_  | _O(n)_ | Medium| good basic, stack, m$, GS, fb, `amazon`| AGAIN************** (5) 
 739| [Daily Temperatures](https://leetcode.com/problems/daily-temperatures/) | [Python](./leetcode_python/Stack/daily-temperatures.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/Stack/DailyTemperatures.java)  | _O(n)_  | _O(n)_ | Medium |LC 739, LC 503, LC 406, LC 496, LC 42, Monotonic stack, good trick,`amazon`| AGAIN******************* (12) (MUST)
 772| [Basic Calculator III](https://leetcode.com/problems/basic-calculator-iii/) |[Python](./leetcode_python/Stack/basic-calculator-iii.py)| _O(n)_| _O(n)_| Medium |check LC 224, 227| AGAIN (not start)
-853| [Car Fleet](https://leetcode.com/problems/car-fleet/)  | [Python](./leetcode_python/Stack/car-fleet.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/Stack/CarFleet.java) | _O(nlogn)_  | _O(n)_| Medium|array, stack, good trick, google, amz| AGAIN***** (2)
+853| [Car Fleet](https://leetcode.com/problems/car-fleet/)  | [Python](./leetcode_python/Stack/car-fleet.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/Stack/CarFleet.java) | _O(nlogn)_  | _O(n)_| Medium|array sorting, good trick, google, amz| AGAIN******* (4)
 856| [Score of Parentheses](https://leetcode.com/problems/score-of-parentheses/) | [Python](./leetcode_python/Stack/score-of-parentheses.py) | _O(n)_  | _O(1)_   | Medium   || AGAIN (not start)
 872| [Leaf-Similar Trees](https://leetcode.com/problems/leaf-similar-trees/) |  [Python](./leetcode_python/Stack/leaf-similar-trees.py),  [Java](./leetcode_java/src/main/java/LeetCodeJava/Stack/LeafSimilarTrees.java)  | _O(n)_  | _O(h)_| Easy|| AGAIN* 
 895| [Maximum Frequency Stack](https://leetcode.com/problems/maximum-frequency-stack/) |  [Python](./leetcode_python/Stack/maximum-frequency-stack.py) | _O(n)_  | _O(h)_| Hard| good basic, heap, design, stack, amazon, apple, linkedin, m$, twitter| AGAIN********** (1) (not start) 

data/progress.txt

@@ -1,4 +1,4 @@
-20241208: 304
+20241208: 304,853
 20241202: 370(todo),1109(todo)
 20241130: 34,767
 20241126: 722,380

data/to_review.txt

@@ -1,4 +1,4 @@
-2025-02-01 -> ['304']
+2025-02-01 -> ['304,853']
 2025-01-26 -> ['370(todo),1109(todo)']
 2025-01-24 -> ['34,767']
 2025-01-20 -> ['722,380']
@@ -7,32 +7,32 @@
 2025-01-16 -> ['776,31']
 2025-01-15 -> ['004(todo),34(todo),162(todo),275(todo)']
 2025-01-14 -> ['986(todo),1229(todo),1868(todo),80(todo),209(todo),283(todo),360(todo),713(todo),532(todo),611(todo)']
-2025-01-11 -> ['304', '394']
+2025-01-11 -> ['304,853', '394']
 2025-01-10 -> ['833,950']
 2025-01-05 -> ['370(todo),1109(todo)']
 2025-01-04 -> ['53,210,207']
 2025-01-03 -> ['34,767', '444']
 2025-01-02 -> ['1188,130,855(again)']
 2024-12-30 -> ['722,380']
-2024-12-29 -> ['304', '33,81']
+2024-12-29 -> ['304,853', '33,81']
 2024-12-28 -> ['900']
 2024-12-27 -> ['253', '26,27', '802,1197,26']
 2024-12-26 -> ['776,31']
 2024-12-25 -> ['004(todo),34(todo),162(todo),275(todo)']
 2024-12-24 -> ['986(todo),1229(todo),1868(todo),80(todo),209(todo),283(todo),360(todo),713(todo),532(todo),611(todo)']
 2024-12-23 -> ['370(todo),1109(todo)']
-2024-12-21 -> ['304', '34,767', '394', '855,846']
+2024-12-21 -> ['304,853', '34,767', '394', '855,846']
 2024-12-20 -> ['833,950', '932']
 2024-12-18 -> ['951,792']
 2024-12-17 -> ['722,380']
-2024-12-16 -> ['304', '33,81']
+2024-12-16 -> ['304,853', '33,81']
 2024-12-15 -> ['370(todo),1109(todo)']
 2024-12-14 -> ['253', '53,210,207', '163,1048']
-2024-12-13 -> ['304', '34,767', '776,31', '444', '298,729']
+2024-12-13 -> ['304,853', '34,767', '776,31', '444', '298,729']
 2024-12-12 -> ['004(todo),34(todo),162(todo),275(todo)', '1188,130,855(again)', '1146']
-2024-12-11 -> ['304', '986(todo),1229(todo),1868(todo),80(todo),209(todo),283(todo),360(todo),713(todo),532(todo),611(todo)']
-2024-12-10 -> ['304', '370(todo),1109(todo)']
-2024-12-09 -> ['304', '722,380']
+2024-12-11 -> ['304,853', '986(todo),1229(todo),1868(todo),80(todo),209(todo),283(todo),360(todo),713(todo),532(todo),611(todo)']
+2024-12-10 -> ['304,853', '370(todo),1109(todo)']
+2024-12-09 -> ['304,853', '722,380']
 2024-12-08 -> ['34,767', '33,81', '394', '737']
 2024-12-07 -> ['370(todo),1109(todo)', '833,950', '900', '686,734,737']
 2024-12-06 -> ['253', '26,27', '802,1197,26', '353']

leetcode_java/src/main/java/LeetCodeJava/Stack/CarFleet.java

@@ -1,14 +1,159 @@
 package LeetCodeJava.Stack;
 
-// https://leetcode.com/problems/car-fleet/
-
 import java.util.*;
 
+// https://leetcode.com/problems/car-fleet/
+/**
+ * 853. Car Fleet
+ * Solved
+ * Medium
+ * Topics
+ * Companies
+ * There are n cars at given miles away from the starting mile 0, traveling to reach the mile target.
+ *
+ * You are given two integer array position and speed, both of length n, where position[i] is the starting mile of the ith car and speed[i] is the speed of the ith car in miles per hour.
+ *
+ * A car cannot pass another car, but it can catch up and then travel next to it at the speed of the slower car.
+ *
+ * A car fleet is a car or cars driving next to each other. The speed of the car fleet is the minimum speed of any car in the fleet.
+ *
+ * If a car catches up to a car fleet at the mile target, it will still be considered as part of the car fleet.
+ *
+ * Return the number of car fleets that will arrive at the destination.
+ *
+ *
+ *
+ * Example 1:
+ *
+ * Input: target = 12, position = [10,8,0,5,3], speed = [2,4,1,1,3]
+ *
+ * Output: 3
+ *
+ * Explanation:
+ *
+ * The cars starting at 10 (speed 2) and 8 (speed 4) become a fleet, meeting each other at 12. The fleet forms at target.
+ * The car starting at 0 (speed 1) does not catch up to any other car, so it is a fleet by itself.
+ * The cars starting at 5 (speed 1) and 3 (speed 3) become a fleet, meeting each other at 6. The fleet moves at speed 1 until it reaches target.
+ * Example 2:
+ *
+ * Input: target = 10, position = [3], speed = [3]
+ *
+ * Output: 1
+ *
+ * Explanation:
+ *
+ * There is only one car, hence there is only one fleet.
+ * Example 3:
+ *
+ * Input: target = 100, position = [0,2,4], speed = [4,2,1]
+ *
+ * Output: 1
+ *
+ * Explanation:
+ *
+ * The cars starting at 0 (speed 4) and 2 (speed 2) become a fleet, meeting each other at 4. The car starting at 4 (speed 1) travels to 5.
+ * Then, the fleet at 4 (speed 2) and the car at position 5 (speed 1) become one fleet, meeting each other at 6. The fleet moves at speed 1 until it reaches target.
+ *
+ *
+ * Constraints:
+ *
+ * n == position.length == speed.length
+ * 1 <= n <= 105
+ * 0 < target <= 106
+ * 0 <= position[i] < target
+ * All the values of position are unique.
+ * 0 < speed[i] <= 106
+ *
+ *
+ *
+ */
+
 public class CarFleet {
 
     // V0
-    // IDEA : STACK + HASH MAP
+    // IDEA: pair position and speed, sorting (gpt)
+    /**
+     * IDEA :
+     *
+     * The approach involves sorting the cars by their starting positions
+     * (from farthest to nearest to the target)
+     * and computing their time to reach the target.
+     * We then iterate through these times to count the number of distinct fleets.
+     *
+     *
+     *
+     * Steps in the Code:
+     * 	1.	Pair Cars with Their Speeds:
+     * 	    •	Combine position and speed into a 2D array cars for easier sorting and access.
+     * 	2.	Sort Cars by Position Descending:
+     * 	    •	Use Arrays.sort with a custom comparator to sort cars from farthest to nearest relative to the target.
+     * 	3.	Calculate Arrival Times:
+     * 	    •	Compute the time each car takes to reach the target using the formula:
+     *
+     *  time = (target - position) / speed
+     *
+     * 	4.	Count Fleets:
+     * 	    •	Iterate through the times array:
+     * 	    •	If the current car’s arrival time is greater than the lastTime (time of the last fleet), it forms a new fleet.
+     * 	    •	Update lastTime to the current car’s time.
+     * 	5.	Return Fleet Count:
+     * 	    •	The number of distinct times that exceed lastTime corresponds to the number of fleets.
+     *
+     */
     public int carFleet(int target, int[] position, int[] speed) {
+        int n = position.length;
+        // Pair positions with speeds and `sort by position in descending order`
+        // cars : [position][speed]
+        int[][] cars = new int[n][2];
+        for (int i = 0; i < n; i++) {
+            cars[i][0] = position[i];
+            cars[i][1] = speed[i];
+        }
+
+        /**
+         * NOTE !!!
+         *
+         *  Sort by position descending (simulate the "car arriving" process
+         */
+        Arrays.sort(cars, (a, b) -> b[0] - a[0]); // Sort by position descending
+
+        // Calculate arrival times
+        double[] times = new double[n];
+        for (int i = 0; i < n; i++) {
+            times[i] = (double) (target - cars[i][0]) / cars[i][1];
+        }
+
+        // Count fleets
+        int fleets = 0;
+        double lastTime = 0;
+        for (double time : times) {
+            /**
+             * 	4.	Count Fleets:
+             * 	•	Iterate through the times array:
+             * 	•	If the current car’s arrival time is greater than the lastTime (time of the last fleet), it forms a new fleet.
+             * 	•	Update lastTime to the current car’s time.
+             */
+            // If current car's time is greater than the last fleet's time, it forms a new fleet
+            if (time > lastTime) {
+                fleets++;
+                lastTime = time;
+            }
+        }
+
+        return fleets;
+    }
+
+    // V0-1
+    // IDEA : HASH MAP + Array sorting
+    /**
+     *  Step 1) calculate all arriving time for all cars and save as map
+     *  Step 2) sort distance array
+     *      - Sorting ensures that cars are processed in the order they reach the target, making it easier to determine fleet formation.
+     *  Step 3) compare previous arrive time and cur arrive time, if can't form a "fleet" then append to fleet
+     *  Step 4) return fleet size
+     *
+     */
+    public int carFleet_0_1(int target, int[] position, int[] speed) {
 
         int[] dist = new int[position.length];
         double[] arrived_time = new double[position.length];
@@ -33,7 +178,6 @@ public int carFleet(int target, int[] position, int[] speed) {
         return fleet.size();
     }
 
-
     // V1
     // https://leetcode.com/problems/car-fleet/solutions/2013259/java-simple-solution-100-faster/
     public int carFleet_2(int target, int[] position, int[] speed) {

leetcode_java/src/main/java/dev/workspace5.java

@@ -4272,6 +4272,72 @@ public int sumRegion(int row1, int col1, int row2, int col2) {
         }
     }
 
+    // LC 853
+    // 3.22 pm - 3.40 pm
+    /**
+     * You are given two integer array position and speed,
+     * both of length n, where position[i] is the starting mile
+     * of the ith car
+     * and speed[i] is the speed of the ith car in miles per hour.
+     *
+     *
+     * A car cannot pass another car, but it can catch up and
+     * then travel next to it at the speed of the slower car.
+     *
+     * A car fleet is a car or cars driving next to each other.
+     * The speed of the car fleet is the `minimum` speed of any car in the fleet.
+     */
+    /**
+     *
+     * Example 1) target = 12, position = [10,8,0,5,3], speed = [2,4,1,1,3], fleet = 0
+     *
+     *  find if there is any overlap "when time = t"
+     *
+     *  -> t = 1, position = [12,12,1,6,6], so fleet = 2
+     *  -> t = 2, position = [x,x,2,x,x], so fleet = 3
+     *
+     *
+     * Example 2) target = 100, position = [0,2,4], speed = [4,2,1],  fleet = 0
+     *
+     *   -> t = 1,  position = [4, 4, 5], fleet = 1
+     *   -> t = 2, position = [6,6,5], fleet = 1
+     *
+     *
+     *  Idea : stack (FILO)
+     */
+    public int carFleet(int target, int[] position, int[] speed){
+
+        // edge case
+        if (position.length == 1){
+            return 1;
+        }
+
+        // map record car (position) and its speed
+        Map<Integer, Integer> map = new HashMap<>();
+        int fleet = 0;
+        Stack<Integer> stack = new Stack<>();
+        //stack.add()
+        for (int idx = 0; idx < position.length; idx++){
+            map.putIfAbsent(position[idx], speed[idx]);
+            stack.add(position[idx]);
+        }
+
+        while(!stack.isEmpty()){
+            int curP = stack.pop();
+            curP += map.get(curP);
+            if (!stack.contains(curP) && curP < target){
+                stack.add(curP);
+            }else{
+
+            }
+        }
+
+
+        System.out.println(">>> stack = " + stack);
+
+        return stack.size();
+    }
+
 
 }