Leetcode 037 解数独 思路清晰 python

class Solution:

    def isValue(self, board, x, y):
        # 检查已经填入的坐标是否和列中有的元素相等
        for i in range(9): 
            if i != x and board[i][y] == board[x][y]:
                return False
        # 检查已经填入的坐标是否和行中有的元素相等
        for j in range(9): 
            if j != y and board[x][j] == board[x][y]:
                return False

        # 检查每个正方形是否符合（粗线框内只有1~9） 
        m, n = 3*(x // 3), 3*(y // 3)  # 这里求出的是3x3网格的左上角的坐标 
        for i in range(3):
            for j in range(3):
                if(i+m != x or j+n != y) and board[i+m][j+n] == board[x][y]:
                    return False  

        return True

    def dfs(self, board):

        for i in range(9):
            for j in range(9):
                if board[i][j] == 0:
                    for k in '123456789':  # 从里面选择一个
                        board[i][j] = int(k)
                        if self.isValue(board, i, j) and self.dfs(board):
                            return True
                        # 回溯
                        board[i][j] = 0
                    # 都不行，说明上次的数字不合理
                    return False
        # 全部便利完，返回True
        return True

while True:
    try:
        board = []
        for i in range(9):
            row = list(map(int, input().split()))
            board.append(row)

        s = Solution()
        s.dfs(board)

        for i in range(9):
            board[i] = list(map(str, board[i]))
            print(' '.join(board[i]))
    except:
        break