N queens

import java.util.*;

public class NQueens {

    public static void solveNQueens(int n) {
        int[] board = new int[n];
        Arrays.fill(board, -1);
        solve(0, board, n);
    }

    private static void solve(int col, int[] board, int n) {
        if (col == n) {
            printBoard(board, n);
            return;
        }

        for (int row = 0; row < n; row++) {
            if (isSafe(board, col, row, n)) {
                board[col] = row;
                solve(col + 1, board, n);
                board[col] = -1;
            }
        }
    }

    private static boolean isSafe(int[] board, int col, int row, int n) {
        for (int i = 0; i < col; i++) {
            if (board[i] == row || Math.abs(board[i] - row) == Math.abs(i - col)) {
                return false;
            }
        }
        return true;
    }

    private static void printBoard(int[] board, int n) {
        for (int i = 0; i < n; i++) {
            StringBuilder sb = new StringBuilder();
            for (int j = 0; j < n; j++) {
                sb.append(board[i] == j ? 'Q' : '.');
            }
            System.out.println(sb.toString());
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the value of n (size of the board): ");
        int n = scanner.nextInt();
        solveNQueens(n);
    }
}