Merge pull request #420 from gitsunmin/main

[gitsunmin] WEEK4 Solution

longest-consecutive-sequence/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/longest-consecutive-sequence
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+const findStreak = (set: Set<number>) => (num: number): number => {
+    if (!set.has(num - 1)) return takeWhile(num, currentNum => set.has(currentNum)).length;
+    return 0;
+};
+
+const takeWhile = (start: number, predicate: (value: number) => boolean): number[] => {
+    const result: number[] = [];
+    let currentNum = start;
+    while (predicate(currentNum)) {
+        result.push(currentNum);
+        currentNum += 1;
+    }
+    return result;
+}
+
+const max = (maxStreak: number, currentStreak: number): number => Math.max(maxStreak, currentStreak);
+
+function longestConsecutive(nums: number[]): number {
+    const numSet = new Set(nums);
+
+    return [...numSet]
+        .map(findStreak(numSet))
+        .reduce(max, 0);
+}

maximum-product-subarray/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/maximum-product-subarray
+ * time complexity : O(n)
+ * space complexity : O(1)
+ */
+function maxProduct(nums: number[]): number {
+    let r = nums[0];
+    let mx = 1, mn = 1;
+
+    for (let i = 0; i < nums.length; i++) {
+        const tempMx = mx * nums[i];
+        const tempMn = mn * nums[i];
+
+        mx = Math.max(tempMx, tempMn, nums[i]);
+        mn = Math.min(tempMx, tempMn, nums[i]);
+
+        r = Math.max(r, mx);
+    }
+
+    return r;
+}

missing-number/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/missing-number
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+function missingNumber(nums: number[]): number {
+    const set = new Set<number>(nums);
+
+    for (let i = 0; i < set.size + 1; i++) if (!set.has(i)) return i;
+
+    return 0;
+};

valid-palindrome/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/valid-palindrome
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+
+const clean = (s: string): string => s.toLowerCase().replace(/[^a-z0-9]/g, "");
+
+const reverse = (s: string): string => s.split("").reverse().join("");
+
+function isPalindrome(s: string): boolean {
+    const cleaned = clean(s);
+    return cleaned === reverse(cleaned);
+};

word-search/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/word-search
+ * time complexity : O(m * n * 4^L)
+ * space complexity : O(L)
+ */
+const dfs = (r: number, c: number, index: number, board: string[][], word: string, rows: number, cols: number): boolean => {
+    if (index === word.length) return true;
+
+    if (r < 0 || r >= rows || c < 0 || c >= cols || board[r][c] !== word[index]) return false;
+    const temp = board[r][c];
+
+    board[r][c] = '🚪';
+    const found = dfs(r + 1, c, index + 1, board, word, rows, cols) ||
+        dfs(r - 1, c, index + 1, board, word, rows, cols) ||
+        dfs(r, c + 1, index + 1, board, word, rows, cols) ||
+        dfs(r, c - 1, index + 1, board, word, rows, cols);
+
+    board[r][c] = temp;
+
+    return found;
+};
+
+function exist(board: string[][], word: string): boolean {
+    const rows = board.length;
+    const cols = board[0].length;
+
+    for (let r = 0; r < rows; r++) {
+        for (let c = 0; c < cols; c++) {
+            if (dfs(r, c, 0, board, word, rows, cols)) return true;
+        }
+    }
+    return false;
+}