使用字符检查二维数组中的特定单词(家庭作业)

def exist(board, word):
    def dfs(board, i, j, word):
        if len(word) == 0:
            return True
        if i < 0 or i >= len(board) or j < 0 or j >= len(board[0]) or board[i][j] != word[0]:
            return False
        temp = board[i][j]
        board[i][j] = "#"
        res = dfs(board, i + 1, j, word[1:]) or dfs(board, i - 1, j, word[1:]) or dfs(board, i, j + 1, word[1:]) or dfs(board, i, j - 1, word[1:])
        board[i][j] = temp
        return res

    for i in range(len(board)):
        for j in range(len(board[0])):
            if dfs(board, i, j, word):
                return True
    return False