leet-q-17.java

class Solution {

  public  boolean solveSudoku(char[][] board) {
    for (int i = 0; i < 9; i++) {
      for (int j = 0; j < 9; j++) {
        if (board[i][j] == '.') {

          for (char c = '1'; c <= '9'; c++) {
            if (isValid(board, i, j, c)) {
              board[i][j] = c;

              if (solveSudoku(board))
                return true;
              else
                board[i][j] = '.';
            }
          }

          return false;
        }
      }
    }
    return true;
  }

  public  boolean isValid(char[][] board, int row, int col, char c) {
    for (int i = 0; i < 9; i++) {
      if (board[i][col] == c)
        return false;

      if (board[row][i] == c)
        return false;

      if (board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c)
        return false;
    }
    return true;
  }
}