37. Sudoku Solver Hard

1/**
2 * [37] Sudoku Solver
3 *
4 * Write a program to solve a Sudoku puzzle by filling the empty cells.
5 * A sudoku solution must satisfy all of the following rules:
6 * <ol>
7 * 	Each of the digits 1-9 must occur exactly once in each row.
8 * 	Each of the digits 1-9 must occur exactly once in each column.
9 * 	Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.
10 * </ol>
11 * The '.' character indicates empty cells.
12 *  
13 * Example 1:
14 * <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png" style="height:250px; width:250px" />
15 * 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"]]
16 * 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"]]
17 * Explanation: The input board is shown above and the only valid solution is shown below:
18 * <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Sudoku-by-L2G-20050714_solution.svg/250px-Sudoku-by-L2G-20050714_solution.svg.png" style="height:250px; width:250px" />
19 * 
20 *  
21 * Constraints:
22 * 
23 * 	board.length == 9
24 * 	board[i].length == 9
25 * 	board[i][j] is a digit or '.'.
26 * 	It is guaranteed that the input board has only one solution.
27 * 
28 */
29pub struct Solution {}
30
31// problem: https://leetcode.com/problems/sudoku-solver/
32// discuss: https://leetcode.com/problems/sudoku-solver/discuss/?currentPage=1&orderBy=most_votes&query=
33
34// submission codes start here
35
36impl Solution {
37    pub fn solve_sudoku(board: &mut Vec<Vec<char>>) {
38        
39    }
40}
41
42// submission codes end
43
44#[cfg(test)]
45mod tests {
46    use super::*;
47
48    #[test]
49    fn test_37() {
50    }
51}
52