leetcode专题训练 79. Word Search

需要注意的就是已经用过的点不能再用，所以要设置一个vis数组来存储是否用过。

class Solution:
    def exist(self, board: List[List[str]], word: str) -> bool:
        if word == '':
            return True
        if board is None:
            return False

        r = len(board)
        c = len(board[0])
        l = len(word)

        # 上：-1， 0
        # 下：1， 0
        # 左：0， -1
        # 右：0， 1
        dirs = [[-1, 0], [1, 0], [0, -1], [0, 1]]
        vis = [[0 for i in range(c)] for j in range(r)]

        def go(curr, curc, now):
            if board[curr][curc] != word[now]:
                return False
            if now == l-1:
                return True

            flag = False
            for dire in dirs:
                tmpx = curr+dire[0]
                tmpy = curc+dire[1]
                if tmpx < 0 or tmpy < 0 or tmpx >= r or tmpy >= c or vis[tmpx][tmpy]:
                    continue
                vis[tmpx][tmpy] = 1
                flag = go(tmpx, tmpy, now+1)
                vis[tmpx][tmpy] = 0
                if flag:
                    break
            return flag
                
        
        flag = False
        for curr in range(r):
            for curc in range(c):
                if board[curr][curc] == word[0]:
                    vis[curr][curc] = 1
                    flag = go(curr, curc, 0)
                    vis[curr][curc] = 0
                if flag:
                    break
            if flag:
                break
        
        return flag