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.

Solution:

public class Solution {
    public void solveSudoku(char[][] board) {
        solve(board);
    }
    public boolean solve(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(solve(board)) return true;
                            board[i][j] = '.';
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }
    public boolean isValid(char[][] board, int i, int j, char c){
        for(int x=0; x<9; x++){
            if(board[x][j]==c) return false;
            if(board[i][x]==c) return false;
            if(board[i/3*3+x/3][j/3*3+x%3]==c) return false;
        }
        return true;
    }
}