[hoyeongkwak\ Week 09 Solutions

linked-list-cycle/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(n)
+Space complexity : O(1)
+*/
+function hasCycle(head: ListNode | null): boolean {
+    let slow = head
+    let fast = head
+
+    while (fast && fast.next) {
+        slow = slow.next
+        fast = fast.next.next
+        if (slow === fast) {
+            return true
+        }
+    }
+    return false
+};

maximum-product-subarray/hoyeongkwak.ts

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+/*
+Time complexity : O(n)
+Space complexity : O(1)
+*/
+function maxProduct(nums: number[]): number {
+    let max = 1
+    let min = 1
+    let result = nums[0]
+    nums.forEach((num) => {
+        const tempMax = Math.max(num, max * num, min * num)
+        min = Math.min(num, max * num, min * num)
+        max = tempMax
+        result = Math.max(result, max)
+    })
+    return result
+}

minimum-window-substring/hoyeongkwak.ts

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+/*
+Time complexity: O(s+t)
+Space complexity: O(s+t)
+*/
+function minWindow(s: string, t: string): string {
+    const targetMap = new Map<string, number>()
+    for (const char of t) {
+        targetMap.set(char, (targetMap.get(char) || 0) + 1)
+    }
+
+    const requiredCnt = targetMap.size
+
+    let left = 0
+    let right = 0
+    let formed = 0
+    const windowCounts = new Map<string, number>()
+
+    let minLen = Infinity
+    let minLeft = 0
+    let minRight = 0
+
+    while (right < s.length) {
+        const rightChar = s[right]
+        windowCounts.set(rightChar, (windowCounts.get(rightChar) || 0) + 1)
+        if (targetMap.has(rightChar) &&
+            windowCounts.get(rightChar) === targetMap.get(rightChar)) {
+            formed++
+        }
+
+        while (left <= right && formed == requiredCnt) {
+            if (right - left + 1 < minLen) {
+                minLen = right - left + 1
+                minLeft = left
+                minRight = right
+            }
+            const leftChar = s[left]
+            windowCounts.set(leftChar, windowCounts.get(leftChar)! - 1)
+
+            if (targetMap.has(leftChar) && windowCounts.get(leftChar)! < targetMap.get(leftChar)) {
+                formed--
+            }
+            left++
+        }
+        right++
+    }
+    return minLen === Infinity ? "" : s.substring(minLeft, minRight + 1)
+};

pacific-atlantic-water-flow/hoyeongkwak.ts

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+/*
+Time complexity : O(m * n)
+Space complexity : O(m * n)
+*/
+function pacificAtlantic(heights: number[][]): number[][] {
+    const m = heights.length
+    const n = heights[0].length
+    const pacific: boolean[][] = Array(m).fill(null).map(() => Array(n).fill(false))
+    const atlantic: boolean[][] = Array(m).fill(null).map(() => Array(n).fill(false))
+
+    const dfs = (row: number, col: number, visited: boolean[][], prevH: number): void => {
+        if (row < 0 || row >= m || col < 0 || col >= n || visited[row][col] || heights[row][col] < prevH) {
+            return
+        }
+        visited[row][col] = true
+        const directions = [[1, 0], [-1, 0], [0, 1], [0, -1]]
+        for (const [dr, dc] of directions) {
+            dfs(row + dr, col + dc, visited, heights[row][col])
+        }
+    }
+
+    for (let row = 0; row < m; row++) {
+        dfs(row, 0, pacific, heights[row][0])
+
+    }
+
+    for (let col = 0; col < n; col++) {
+        dfs(0, col, pacific, heights[0][col])
+    }
+
+     for (let row = 0; row < m; row++) {
+        dfs(row, n - 1, atlantic, heights[row][n - 1])
+    }
+
+    for (let col = 0; col < n; col++) {
+        dfs(m - 1, col, atlantic, heights[m - 1][col])
+    }
+
+    const result: number[][] = []
+    for (let row = 0; row < m; row++) {
+        for (let col = 0; col < n; col++) {
+            if (pacific[row][col] && atlantic[row][col]) {
+                result.push([row, col])
+            }
+        }
+    }
+    return result
+};

sum-of-two-integers/hoyeongkwak.ts

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+/*
+Time complexity : O(1)
+Space complexity : O(1)
+*/
+function getSum(a: number, b: number): number {
+    let xor = a ^ b
+    let carry = (a & b) << 1
+
+    while (carry !== 0) {
+        const tempXor = xor ^ carry
+        carry = (xor & carry) << 1
+        xor = tempXor
+    }
+    return xor
+};