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g0001_0100.s0037_sudoku_solver.readme.md Maven / Gradle / Ivy

37\. Sudoku Solver

Hard

Write a program to solve a Sudoku puzzle by filling the empty cells.

A sudoku solution must satisfy **all of the following rules**:

1.  Each of the digits `1-9` must occur exactly once in each row.
2.  Each of the digits `1-9` must occur exactly once in each column.
3.  Each of the digits `1-9` must occur exactly once in each of the 9 `3x3` sub-boxes of the grid.

The `'.'` character indicates empty cells.

**Example 1:**

![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png)

**Input:** 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"]]

**Output:** [["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"]]

**Explanation:** The input board is shown above and the only valid solution is shown below: ![](https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Sudoku-by-L2G-20050714_solution.svg/250px-Sudoku-by-L2G-20050714_solution.svg.png)

**Constraints:**

*   `board.length == 9`
*   `board[i].length == 9`
*   `board[i][j]` is a digit or `'.'`.
*   It is **guaranteed** that the input board has only one solution.