37. 解数独 - 力扣（LeetCode）

思路：

class Solution(object):
    def back(self,board):
        for i in range(len(board)):
            for j in range(len(board[0])):
                if board[i][j] != '.':
                    continue
                for k in range(1,10):
                    if self.isValid(i,j,k,board):
                        board[i][j]=str(k)
                        if self.back(board):
                            return True
                        board[i][j]='.'
                return False
        return True

    def isValid(self,row,col,num,board):
        word=str(num)
        for i in range(9):
            if board[row][i]==word:
                return False
        for i in range(9):
            if board[i][col]==word:
                return False
        startRow=(row/3)*3
        startCol=(col/3)*3
        for i in range(startRow,startRow+3):
            for j in range(startCol,startCol+3):
                if board[i][j]==word:
                    return False
        return True
        
    def solveSudoku(self, board):
        self.back(board)