LeetCode Sudoku Solver

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

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

public class Solution {

     public void solveSudoku(char[][] board) {
         doSolveSudoku(board);
     }
     private boolean doSolveSudoku(char[][] board) {
         for (int i = 0; i < 9; i++) {
             for (int j = 0; j < 9; j++) {
                 if ('.' == board[i][j]) {
                     for (int k = 1; k <= 9; k++) {
                         board[i][j] = (char) ('0' + k);
                         if (isValid(board, i, j)) {
                             if (doSolveSudoku(board)) {
                                 return true;
                             }
                         }
                         board[i][j]='.';
                     }
                     return false;
                 }
             }
         }
         return true;
     }
     private boolean isValid(char[][] board, int x, int y) {
         int row,col;
         for (row = 0; row < 9; row++) {
             if ((x != row) && (board[row][y] == board[x][y])) {
                 return false;
             }
         }
         for (col = 0; col < 9; col++) {
             if ((y != col) && (board[x][y] == board[x][col])) {
                 return false;
             }
         }
         for (row = (x/3)*3; row <(x/3+1)*3 ; row++) {
             for (col = (y/3)*3; col <(y/3+1)*3 ; col++) {
                 if ((x != row) && (y != col) && (board[x][y] == board[row][col])) {
                     return false;
                 }
             }
         }
         return true;
     }
}