NQueens.java

/*1. You are given a number n, the size of a chess board.
2. You are required to place n number of queens in the n * n cells of board such that no queen can kill another.
Note - Queens kill at distance in all 8 directions
3. Complete the body of printNQueens function - without changing signature - to calculate and print all safe configurations of n-queens. Use sample input and output to get more idea.
*/
import java.io.*;
import java.util.*;

public class Main {

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        int[][] chess = new int[n][n];
        printNQueens(chess, "", 0);
    }

    public static void printNQueens(int[][] chess, String qsf, int row){
        if(row == chess.length){
            System.out.println(qsf + ".");
            return;
        }
        for(int col = 0; col < chess.length; col++){
            if(chess[row][col] == 0 && isQueenSafe(chess, row, col) == true){
                chess[row][col] = 1;
                printNQueens(chess, qsf + row + "-" + col + ", ", row + 1);
                chess[row][col] = 0;
            }
        }
    }

    public static boolean isQueenSafe(int[][] chess, int row, int col){
        for(int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--){
            if(chess[i][j] == 1){
                return false;
            }
        }

        for(int i = row - 1, j = col; i >= 0; i--){
            if(chess[i][j] == 1){
                return false;
            }
        }

        for(int i = row - 1, j = col + 1; i >= 0 && j < chess.length; i--, j++){
            if(chess[i][j] == 1){
                return false;
            }
        }

        // for(int i = row, j = col - 1; j >= 0; j--){
        //     if(chess[i][j] == 1){
        //         return false;
        //     }
        // }

        return true;
    }