8 Queens' problem (Backtracked).java

import java.util.Arrays;

public class NQueens {


    private static boolean nQueens(int[][] board, int col) {
        if (col >= board.length) {
            return true;
        }

        for (int row = 0; row < board.length; row++) {
            if (isSafe(board, row, col)) {
                board[row][col] = 1;

                // If successfully put the next queen
                if (nQueens(board, col + 1)) {
                    return true;
                }

                // Backtrack
                board[row][col] = 0;
            }
        }
        return false;
    }


    private static boolean isSafe(int[][] board, int row, int col) {
        for (int j = 0; j < col; j++) {
            if (board[row][j] == 1) {
                return false;
            }
        }

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

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

        return true;
    }


    public static void printSoln(int[][] board) {
        for (int i = 0; i < board.length; i++) {
            System.out.println(Arrays.toString(board[i]));
        }
    }


    public static void main(String[] args) {

        int[][] board = new int[8][8];

        if (!nQueens(board, 0)) {
            System.out.println("No such solution can be found.");
            return;
        }

        printSoln(board);
    }

}