sudokusolver.java

public class sudokusolver {

    public boolean isSafe(char[][] board, int row, int col, int n){
        for (int i = 0 ; i <board.length ; i++){
            if (board[i][col] == (char) (n + '0')){
                return false;
            }
            if (board[row][i] == (char)(n+'0')) {
                return false;
            }
        }
        int sr = (row/3) * 3 ; 
        int sc = (col/3) * 3 ;
        for (int i = sr; i<sr+3; i++){
            for (int j = sc; j<sc+3; j++){
                if (board[i][j] == (char) (n+'0')) {
                    return false;
                }
            }
        }
        return true;
    }

    public boolean helper(char[][] board, int row , int col){
        if (row == board.length ) {
            return true;
        }
        int newrow = 0;
        int newcol = 0;
        if (col != board.length) {
            newcol = col + 1;
        }else{
            newrow += 1; 
            newcol = 0;
        }
        if (board[row][col] != '.') {
            if(helper(board, newrow, newcol)){
                return true;
            }
        }else{
            for (int i = 0 ; i<=9; i++){
                if (isSafe(board , row, col,i )){
                    board[row][col] = (char)(i + '0');
                    if(helper(board, newrow, newcol)){
                        return true;
                    }else{
                        board[row][col] = '.';
                    }
                }
            }
        }
        return false;
    }
    public void sudokusolver(char[][] baord){
        char [][] board = new char[3][3];  // user can write there board here.
        helper(board, 0, 0);
    }
}