word-search

word-search/taewanseoul.ts

@@ -0,0 +1,53 @@
+/**
+ * 268. Missing Number
+ * 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.
+ *
+ * https://leetcode.com/problems/word-search/description/
+ */
+
+// O(4^n) time
+// O(n) space
+function exist(board: string[][], word: string): boolean {
+  let result = false;
+  const num_rows = board.length;
+  const num_cols = board[0].length;
+
+  function checkNeighbors(
+    board: (string | null)[][],
+    word: string,
+    row: number,
+    col: number,
+    startIndex: number
+  ) {
+    const num_rows = board.length;
+    const num_cols = board[0].length;
+
+    if (row < 0 || row >= num_rows || col < 0 || col >= num_cols) return;
+
+    if (board[row][col] !== word[startIndex]) return;
+
+    if (startIndex === word.length - 1) {
+      result = true;
+      return;
+    }
+
+    board[row][col] = null;
+    checkNeighbors(board, word, row + 1, col, startIndex + 1);
+    checkNeighbors(board, word, row - 1, col, startIndex + 1);
+    checkNeighbors(board, word, row, col + 1, startIndex + 1);
+    checkNeighbors(board, word, row, col - 1, startIndex + 1);
+    board[row][col] = word[startIndex];
+  }
+
+  for (let i = 0; i < num_rows; i++) {
+    for (let j = 0; j < num_cols; j++) {
+      if (board[i][j] === word[0]) {
+        checkNeighbors(board, word, i, j, 0);
+        if (result) return result;
+      }
+    }
+  }
+
+  return result;
+}