WEEK 4 Solutions

Author: hoyeongkwak

coin-change/hoyeongkwak.ts

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+function coinChange(coins: number[], amount: number): number {
+    /*
+    O(n)
+    O(n)
+    */
+    if (amount === 0) return 0
+
+    const dp = new Array(amount + 1).fill(Infinity)
+    dp[0] = 0
+    for(let coin of coins) {
+        for (let idx = coin; idx <= amount; idx++) {
+            dp[idx] = Math.min(dp[idx], dp[idx - coin] + 1)
+        }
+    }
+    if (dp[amount] === Infinity) {
+        return -1
+    } else {
+        return dp[amount]
+    }
+};

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

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+function findMin(nums: number[]): number {
+    /*
+    space complexity: 1
+    time complexity : nlogn
+    */
+    // return nums.sort((a, b) => a - b)[0]
+
+    /*
+    space complexity: 1
+    time complexity : logn
+    */
+    let left = 0
+    let right = nums.length - 1
+
+    while (left < right) {
+        const mid = left + Math.floor((right - left) / 2)
+        if (nums[mid] > nums[right]) {
+            left = mid + 1
+        } else {
+            right = mid
+        }
+    }
+    return nums[left]
+};

maximum-depth-of-binary-tree/hoyeongkwak.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)
+ *     }
+ * }
+ */
+
+/* 
+    time complexity : O(n)
+    space complexity : O(logn)
+*/
+
+function maxDepth(root: TreeNode | null): number {
+    if (root == null) return 0
+    let maxLeft = maxDepth(root.left)
+    let maxRight = maxDepth(root.right)
+    return Math.max(maxLeft, maxRight) + 1
+};

merge-two-sorted-lists/hoyeongkwak.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)
+ *     }
+ * }
+ */
+
+/* 
+    time complexity : O(m + n)
+    space complexity : O(m + n)
+*/
+
+function mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
+    if (list1 == null) return list2
+    if (list2 == null) return list1
+
+    if (list1.val < list2.val) {
+        list1.next = mergeTwoLists(list1.next, list2)
+        return list1
+    } else {
+        list2.next = mergeTwoLists(list1, list2.next)
+        return list2
+    }
+
+};

word-search/hoyeongkwak.ts

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+function exist(board: string[][], word: string): boolean {
+    /*
+    O(m * n)
+    O(m * n)
+    */
+    const rowsLen = board.length
+    const colsLen = board[0].length 
+    const direction = [[0, 1], [1, 0], [0, -1], [-1, 0]]
+    const visited = Array(rowsLen).fill(0).map(() => Array(colsLen).fill(false))
+    const dfs = (row: number, col: number, idx: number): boolean => {
+        if (idx === word.length)
+            return true
+        if (row < 0 || row >= rowsLen || col < 0 || 
+        col >= colsLen || board[row][col] !== word[idx] || visited[row][col])
+            return false    
+        visited[row][col] = true
+        if (idx === word.length - 1) return true
+        for (const [dx, dy] of direction) {
+            const newRow = row + dx
+            const newCol = col + dy
+
+            if (newRow >= 0 && newRow < rowsLen && newCol >= 0 && newCol < colsLen && !visited[newRow][newCol] && board[newRow][newCol] === word[idx + 1]) {
+                if (dfs(newRow, newCol, idx + 1)) {
+                    return true
+                }
+            }
+        }
+        visited[row][col] = false
+        return false
+    }
+
+    for (let r = 0; r < rowsLen; r++) {
+        for(let c = 0; c < colsLen; c++) {
+            if (board[r][c] === word[0] && dfs(r, c, 0)) {
+                return true
+            }
+        }
+    }
+    return false
+};