feat: add Word Search

Author: dukeluo

README.md

@@ -76,6 +76,7 @@ Roadmap: https://neetcode.io/roadmap
 | 39   | [Combination Sum](https://leetcode.com/problems/combination-sum/description/)                                                                                     | Medium     | [ts](./TypeScript/39.combination-sum.ts)                                                      | Backtracking     |
 | 90   | [Subsets II](https://leetcode.com/problems/subsets-ii/description/)                                                                                               | Medium     | [ts](./TypeScript/90.subsets-ii.ts)                                                           | Backtracking     |
 | 40   | [Combination Sum II](https://leetcode.com/problems/combination-sum-ii/description/)                                                                               | Medium     | [ts](./TypeScript/40.combination-sum-ii.ts)                                                   | Backtracking     |
+| 79   | [Word Search](https://leetcode.com/problems/word-search/)                                                                                                         | Medium     | [ts](./TypeScript/79.word-search.ts)                                                          | Backtracking     |
 
 ### Others
 

TypeScript/79.word-search.ts

@@ -0,0 +1,63 @@
+function exist(board: string[][], word: string): boolean {
+  const rows = board.length;
+  const cols = board[0].length;
+  const paths = new Set<string>();
+
+  function backtrace(r: number, c: number, i: number) {
+    if (i === word.length) {
+      return true;
+    }
+
+    if (
+      r < 0 ||
+      r >= rows ||
+      c < 0 ||
+      c >= cols ||
+      board[r][c] !== word[i] ||
+      paths.has(`${r}, ${c}`)
+    ) {
+      return false;
+    }
+
+    paths.add(`${r}, ${c}`);
+    const result =
+      backtrace(r + 1, c, i + 1) ||
+      backtrace(r - 1, c, i + 1) ||
+      backtrace(r, c + 1, i + 1) ||
+      backtrace(r, c - 1, i + 1);
+    paths.delete(`${r}, ${c}`);
+
+    return result;
+  }
+
+  for (let i = 0; i < rows; i++) {
+    for (let j = 0; j < cols; j++) {
+      if (backtrace(i, j, 0)) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+console.log(
+  exist(
+    [
+      ["A", "B", "C", "E"],
+      ["S", "F", "C", "S"],
+      ["A", "D", "E", "E"],
+    ],
+    "ABCCED"
+  )
+);
+console.log(
+  exist(
+    [
+      ["A", "B", "C", "E"],
+      ["S", "F", "C", "S"],
+      ["A", "D", "E", "E"],
+    ],
+    "SEE"
+  )
+);