Description:
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.
算法分析：
这题可以采用回溯法。
本题找到解的处理是return true，因此返回值为bool。
对于每个空位'.'，遍历1~9，check合理之后往下一个位置递归。
由于这里路径尝试本质上是有序的，即1~9逐个尝试，因此无需额外设置状态位记录已经尝试过的方向。
注意：只有正确达到最终81位置（即成功填充）的填充结果才可以返回，若不然，将会得到错误的填充。
因此辅助函数solve需要设为bool而不是void。
代码如下：
__author__ = 'andy' class Solution: # @param board, a 9x9 2D array # Solve the Sudoku by modifying the input board in-place. # Do not return any value. def check(self, x, y, board): tmp = board[x][y] board[x][y] = '.' for row in range(9): if board[row][y] == tmp: return False for col in range(9): if board[x][col] == tmp: return False for row in range(3): for col in range(3): if board[(x / 3) * 3 + row][(y / 3) * 3 + col] == tmp: return False board[x][y] = tmp return True def dfs(self, board): for row in range(9): for col in range(9): if board[row][col] == '.': for char in '123456789': board[row][col] = char if self.check(row, col, board) and self.dfs(board): return True board[row][col] = '.' return False return True def solveSudoku(self, board): self.dfs(board)
