原题地址：https://oj.leetcode.com/problems/sudoku-solver/
题意：
Write a program to solve a Sudoku puzzle by filling the empty cells.
Empty cells are indicated by the character ‘.‘.
You may assume that there will be only one unique solution.
A sudoku puzzle...
...and its solution numbers marked in red.
解题思路：使用dfs来解决问题。
代码：
class Solution: # @param board, a 9x9 2D array # Solve the Sudoku by modifying the input board in-place. # Do not return any value. def solveSudoku(self, board): def isValid(x,y): tmp=board[x][y]; board[x][y]=‘D‘ for i in range(9): if board[i][y]==tmp: return False for i in range(9): if board[x][i]==tmp: return False for i in range(3): for j in range(3): if board[(x/3)*3+i][(y/3)*3+j]==tmp: return False board[x][y]=tmp return True def dfs(board): for i in range(9): for j in range(9): if board[i][j]==‘.‘: for k in ‘123456789‘: board[i][j]=k if isValid(i,j) and dfs(board): return True board[i][j]=‘.‘ return False return True dfs(board)