Feat: 79. Word Search

Author: HC-kang

word-search/HC-kang.ts

@@ -1,3 +1,57 @@
+/**
+ * https://leetcode.com/problems/word-search
+ * T.C. O(n * m * 4^l)
+ * S.C. O(n * m)
+ */
 function exist(board: string[][], word: string): boolean {
+  const countMap = new Map<string, number>();
+
+  for (let i = 0; i < word.length; i++) {
+    countMap.set(word[i], (countMap.get(word[i]) || 0) + 1);
+  }
+  for (let i = 0; i < board.length * board[0].length; i++) {
+    countMap.set(board[Math.floor(i / board[0].length)][i % board[0].length], 0);
+  }
+
+  if (Array.from(countMap.values()).some((v) => v > 0)) return false;
+
+  let seen = Array.from({ length: board.length }, () =>
+    new Array(board[0].length).fill(false)
+  );
+  const directives = [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ];
+
+  function dfs(h: number, w: number, index: number): boolean {
+    if (w < 0 || w >= board[0].length) return false;
+    if (h < 0 || h >= board.length) return false;
+
+    if (seen[h][w]) return false;
+    if (board[h][w] !== word[index]) return false;
+    if (index === word.length - 1) return true;
+
+    seen[h][w] = true;
+
+    for (let i = 0; i < 4; i++) {
+      const [dh, dw] = directives[i];
+      if (dfs(h + dh, w + dw, index + 1)) {
+        return true;
+      }
+    }
+
+    seen[h][w] = false;
+    return false;
+  }
+
+  for (let i = 0; i < board.length; i++) {
+    for (let j = 0; j < board[0].length; j++) {
+      if (dfs(i, j, 0)) {
+        return true;
+      }
+    }
+  }
   return false;
 }