单词搜素 python

# 给定一个 m x n 二维字符网格 board 和一个字符串单词 word 。如果 word 存在于网格中，返回 true ；否则，返回 false 。 
# 
#  单词必须按照字母顺序，通过相邻的单元格内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母不允许被重复使用。 
# 
#  
# 
#  示例 1： 
# 
#  
# 输入：board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "AB
# CCED"
# 输出：true

方法：深度优先

def findWords(board, word):
    if not board or not word:
        return False
    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 word[0] != board[i][j]:
            return False
        tmp = 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] = tmp
        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