[79] 单词搜索

/**
 * @param {character[][]} board
 * @param {string} word
 * @return {boolean}
 */
var exist = function (board, word) {
  const yLen = board.length
  const xLen = board[0].length
  const wLen = word.length
  const matrix = Array.from(Array(yLen), () => new Array(xLen).fill(true))
  //方向 左、右、上、下
  const direction = [
    { dirX: 1, dirY: 0 },
    { dirX: -1, dirY: 0 },
    { dirX: 0, dirY: 1 },
    { dirX: 0, dirY: -1 },
  ]
  const inArea = (x, y) => {
    return x >= 0 && x < xLen && y >= 0 && y < yLen && matrix[y][x]
  }
  const isAns = (x, y, index) => {
    if (board[y][x] !== word[index]) {
      return false
    }
    index++;
    if (index === wLen) {
      return true
    }
    matrix[y][x] = false;
    for (let i = 0; i < direction.length; i++) {
      const newX = x + direction[i].dirX
      const newY = y + direction[i].dirY
      if (inArea(newX, newY) && isAns(newX, newY, index)) {
        return true
      }
    }
    index--;
    matrix[y][x] = true;
    return false;
  }
  for (let x = 0; x < xLen; x++) {
    for (let y = 0; y < yLen; y++) {
      if (isAns(x, y, 0)) {
        return true;
      }
    }
  }
  return false;
};