【LeetCode】37. Sudoku Solver 解题报告（Python）

题目分析：

这一题很容易想到八（N）皇后问题，而且判断是否成立可以借用【LeetCode】36. Valid Sudoku题的方法。这样我们使用双循环找一个为值’.‘的位置循环换成1-9，判断换前与还后都成立就标记为True，否则还至为’.’。
测试代码：

class Solution:
    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[int(x/3)*3+i][int(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)

print(Solution().solveSudoku([
  ["5","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]))  # 提交时请删除print

参考博客