Leetcode - 37. 解数独

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：

1. 数字1-9在每一行只能出现一次。
2. 数字1-9在每一列只能出现一次。
3. 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
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标签：数字,示例,37,length,board,输入,解数,Leetcode,数独
来源： https://www.cnblogs.com/Code2235/p/15216304.html