[j2h30728] WEEK 04 Solutions (#2760)

* week4: 104. Maximum Depth of Binary tree

* week4: 21. Merge Two Sorted Lists

* week4: 153. Find Minimum in Rotated Sorted Array

* week4: 322. Coin Change

* fix: add trailing newline to week4 solution files

Author: j2h30728

coin-change/j2h30728.ts

@@ -0,0 +1,14 @@
+function coinChange(coins: number[], amount: number): number {
+  const dp = new Array(amount + 1).fill(amount + 1);
+    dp[0] = 0;
+    
+    for (let i = 1; i <= amount; i++) {
+        for (const coin of coins) {
+            if (i - coin >= 0) {
+                dp[i] = Math.min(dp[i], 1 + dp[i - coin]);
+            }
+        }
+    }
+    
+    return dp[amount] > amount ? -1 : dp[amount];
+};

find-minimum-in-rotated-sorted-array/j2h30728.ts

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+function findMin(nums: number[]): number {
+    const n = nums.length - 1;
+    let last = nums[n];
+    let left = 0, right = n;
+    
+    while(left < right){
+        const mid = (left + right) >> 1;
+        if(nums[mid] > last) left = mid + 1;
+        else right = mid;
+    }
+    return nums[left];
+};

maximum-depth-of-binary-tree/j2h30728.ts

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+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+function maxDepth(root: TreeNode | null): number {
+    if(!root) return 0;
+    const maxLeft = maxDepth(root.left);
+    const maxRight = maxDepth(root.right);
+    return Math.max(maxLeft, maxRight) + 1;
+};

merge-two-sorted-lists/j2h30728.ts

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+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
+    const root = new ListNode();
+    let tail = root;
+    
+    while(list1 !== null && list2 !== null){
+        if(list1.val <= list2.val){
+            tail.next = list1;
+            list1 = list1.next;
+        }else{
+            tail.next = list2;
+            list2 = list2.next;
+        }
+        tail = tail.next;
+    }
+    tail.next = list1 !== null ? list1 : list2;
+    return root.next;
+};