feat: 单词搜索

Author: sl1673495

递归与回溯/单词搜索-79.js

@@ -0,0 +1,64 @@
+/**
+ * @param {character[][]} board
+ * @param {string} word
+ * @return {boolean}
+ */
+let directions = [[-1, 0], [1, 0], [0, -1], [0, 1]] // 左 右 上 下
+
+let exist = function (board, word) {
+    let maxY = board.length
+    if (!maxY) return false
+    let maxX = board[0].length
+
+    // 二维数组记录已访问过的元素
+    let visited = new Array(maxY)
+    for (let y = 0; y < visited.length; y++) {
+        visited[y] = new Array(maxX)
+    }
+
+    let inArea = (x, y) => {
+        return x >= 0 && x < maxX && y >= 0 && y < maxY
+    }
+
+    let search = (startX, startY, wordIndex) => {
+        // 当前起始字符不匹配 直接失败
+        let curCell = board[startY][startX]
+        let curChar = word[wordIndex]
+        if (curCell !== curChar) {
+            return false
+        }
+
+        // 如果递归到最后一位字符 就直接返回最后一位字符是否匹配成功
+        if (wordIndex === word.length - 1) {
+            return curChar === curChar
+        }
+
+        // 进一步递归 先记录为已访问元素 防止递归的时候重复访问
+        visited[startY][startX] = true
+
+        for (let direction of directions) {
+            let [x, y] = direction
+            let nextX = startX + x
+            let nextY = startY + y
+
+            // 需要保证未越界且未被访问过
+            if (inArea(nextX, nextY) && !visited[nextY][nextX]) {
+                if (search(nextX, nextY, wordIndex + 1)) {
+                    return true
+                }
+            }
+        }
+        // 重置已访问标记位
+        visited[startY][startX] = false
+    }
+
+    for (let y = 0; y < maxY; y++) {
+        for (let x = 0; x < maxX; x++) {
+            if (search(x, y, 0)) {
+                return true
+            }
+        }
+    }
+
+    return false
+};