python实现 LeetCode37——Sudoku Solver

数独游戏，用了dfs的深度优先树。
25行和26行的else将该位置改为点，是在一次dfs中的，相当于在for循环中不断尝试c值中的赋值。
如果所有的c值都不对的时候会进入27行的return false，然后再进入23行的赋值。class Solution(object):
def solveSudoku(self, board):
def isvaild(i,j):
for m in range(9):
if m!=i and board[m][j]==board[i][j]:
return False
for n in range(9):
if n!=j and board[i]
==board[i][j]:
return False
for m in range(i/3*3,i/3*3+3):
for n in range(j/3*3,j/3*3+3):
if m!=i and n!=j and board[m]
==board[i][j]:
return False
return True
for i in range(9):
for j in range(9):
if board[i][j]=='.':
for c in '123456789':
board[i][j]=c
if isvaild(i,j):
if self.solveSudoku(board):
return True
else:
board[i][j] = '.'
else:
board[i][j] = '.'
return False
return True