leetcode 79.单词搜索(python)
给定一个二维网格和一个单词，找出该单词是否存在于网格中。
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:
board =
[
['A','B','C','E'],
['S','F','C','S'],
['A','D','E','E']
]
给定 word = "ABCCED", 返回 true
给定 word = "SEE", 返回 true
给定 word = "ABCB", 返回 false
提示：
board 和 word 中只包含大写和小写英文字母。1 <= board.length <= 2001 <= board[i].length <= 2001 <= word.length <= 10^3
回溯
class Solution(object):
def exist(self
, board
, word
):
if not board
:
return False
for i
in range(len(board
)):
for j
in range(len(board
[0])):
if self
.dfs
(board
, i
, j
, word
):
return True
return False
def dfs(self
, 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
= self
.dfs
(board
, i
+1, j
, word
[1:]) or self
.dfs
(board
, i
-1, j
, word
[1:]) \
or self
.dfs
(board
, i
, j
+1, word
[1:]) or self
.dfs
(board
, i
, j
-1, word
[1:])
board
[i
][j
] = tmp
return res
