1
class Solution {
2
  public void solveSudoku(char[][] board) {
3
    solve(board);
4
  }
5

6
  boolean solve(char board[][]) {
7
    for (int i = 0; i < board.length; i++) {
8
      for (int j = 0; j < board[0].length; j++) {
9
        if (board[i][j] == '.') {
10
          for (char c = '1'; c <= '9'; c++) {
11
            if (isValid(board, c, i, j) == true) {
12
              board[i][j] = c;
13

14
              if (solve(board) == true) return true;
15
              else board[i][j] = '.';
16
            }
17
          }
18
          return false;
19
        }
20
      }
21
    }
22
    return true;
23
  }
24

25
  boolean isValid(char board[][], char c, int row, int col) {
26
    for (int i = 0; i < 9; i++) {
27
      if (board[row][i] == c) return false;
28
      if (board[i][col] == c) return false;
29
      if (board[3 * (row / 3) + (i / 3)][3 * (col / 3) + (i % 3)] == c) return false;
30
    }
31
    return true;
32
  }
33
}