Add JS solution for word search LC medium

Author: nwthomas

src/leetcode/medium/word-search/wordSearch.js

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+/*
+https://leetcode.com/problems/word-search
+
+Given an m x n grid of characters board and a string word, return true if word exists in the grid.
+
+The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.
+
+Example 1:
+Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
+Output: true
+
+Example 2:
+Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "SEE"
+Output: true
+Example 3:
+Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCB"
+Output: false
+
+Constraints:
+m == board.length
+n = board[i].length
+1 <= m, n <= 6
+1 <= word.length <= 15
+board and word consists of only lowercase and uppercase English letters.
+
+Follow up: Could you use search pruning to make your solution faster with a larger board?
+*/
+
+const wordSearch = (board, word) => {
+    function dfs(y, x, i, cache = {}) {
+        if (cache[`${y}${x}`]) {
+            return false;
+        }
+        if (y < 0 || y > board.length - 1 || x < 0 || x > board[0].length - 1) {
+            return false;
+        }
+        if (board[y][x] !== word[i]) {
+            return false;
+        }
+        if (board[y][x] === word[word.length - 1] && i === word.length - 1) {
+            return true;
+        }
+
+        cache[`${y}${x}`] = true;
+
+        const results = [
+            dfs(y - 1, x, i + 1, { ...cache }),
+            dfs(y + 1, x, i + 1, { ...cache }),
+            dfs(y, x - 1, i + 1, { ...cache }),
+            dfs(y, x + 1, i + 1, { ...cache }),
+        ];
+
+        return results.some((result) => result);
+    }
+
+    for (let y = 0; y < board.length; y++) {
+        for (let x = 0; x < board[y].length; x++) {
+            if (board[y][x] === word[0]) {
+                const result = dfs(y, x, 0);
+                if (result) {
+                    return true;
+                }
+            }
+        }
+    }
+
+    return false;
+};
+
+module.exports = { wordSearch };

src/leetcode/medium/word-search/wordSearch.test.js

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+const { wordSearch } = require("./wordSearch");
+
+describe("wordSearch", () => {
+    it("should return true if the word is found in the board", () => {
+        const board = [
+            ["A", "B", "C", "E"],
+            ["S", "F", "C", "S"],
+            ["A", "D", "E", "E"],
+        ];
+        const word = "ABCCED";
+        expect(wordSearch(board, word)).toBe(true);
+    });
+
+    it("should return true if the word is found in the board", () => {
+        const board = [
+            ["A", "B", "C", "E"],
+            ["S", "F", "C", "S"],
+            ["A", "D", "E", "E"],
+        ];
+        const word = "SEE";
+        expect(wordSearch(board, word)).toBe(true);
+    });
+
+    it("should return false if the word is not found in the board", () => {
+        const board = [
+            ["A", "B", "C", "E"],
+            ["S", "F", "C", "S"],
+            ["A", "D", "E", "E"],
+        ];
+        const word = "ABCB";
+        expect(wordSearch(board, word)).toBe(false);
+    });
+});