0037解数独 Marathon

编写一个程序，通过填充空格来解决数独问题。

数独的解法需 遵循如下规则：

数字 1-9 在每一行只能出现一次。
数字 1-9 在每一列只能出现一次。
数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图）
数独部分空格内已填入了数字，空白格用 '.' 表示。

示例：

输入：board = [["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"]]
输出：[["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],["4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9","6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4","5","2","8","6","1","7","9"]]
解释：输入的数独如上图所示，唯一有效的解决方案如下所示：

提示：

board.length == 9
board[i].length == 9
board[i][j] 是一位数字或者 '.'
题目数据 保证 输入数独仅有一个解

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/sudoku-solver

思考：

• https://leetcode-cn.com/problems/sudoku-solver/solution/37-jie-shu-du-hui-su-sou-suo-suan-fa-xiang-jie-by-/

python

# 0037.解数独

class Solution:
    def solveSudoku(self, board:[[str]]):
        def backTrack(board):
            for i in range(len(board)):# 行
                for j in range(len(board[0])): # 列
                    if board[i][j] != ".":continue
                    for k in range(1,10): # (i,j)位置放k是否合适
                        if isValid(i,j,k,board):
                            board[i][j] = str(k)
                            if backTrack(board):return True
                            board[i][j] = "." # 回溯
                    return False # 9个数试完了，都不行
            return True # 遍历完，没有返回False，说明找到合适棋盘位置

        def isValid(row, col, val, board):
            for i in range(9): # 判断行里重复
                if board[row][i] == str(val):
                    return False
            for j in range(9): # 判断列里重复
                if board[j][col] == str(val):
                    return False
            startRow = (row//3) * 3
            startCol = (col//3) * 3
            for i in range(startRow, startRow+3): # 判断9方格是否重复
                for j in range(startCol, startCol+3):
                    if board[i][j] == str(val):
                        return False
            return True

        backTrack(board)

golang

待完善