Time limit exceed

#1

the code is working for the 4 testcase but showing the tle for one testcase

#2

@shudhanshu20092001_af6f20d24c617008
use this approach

  1. Start in the leftmost column .
  2. If all queens are placed return true .
  3. Try all rows in the current column. Do following for every tried row.
  • If the queen can be placed safely in this row then mark this [row, column] as part of the solution and recursively check if placing queen here leads to a solution.
  • If placing the queen in [row, column] leads to a solution then return true.
  • If placing queen doesn’t lead to a solution then umark this row, column and go to step (a) to try other rows.
  • If all rows have been tried and nothing worked, return false to trigger backtracking.

Benchmark your code with my code :

import java.util.*;

public class Main {

    public static void main(String[] args) {
    Scanner scn = new Scanner(System.in);
    int n=scn.nextInt();
        System.out.println(countNquens(n));

    }
    public static int countNquens(int n) {
        boolean[][] board = new boolean[n][n];
        return countNqueens(board, 0);
    }

    public static int countNqueens(boolean[][] board, int row) {
        if (row == board.length) {
            return 1;
        }
        int count = 0;
        for (int col = 0; col < board[row].length; col++) {
            if (isitsafetpq(board, row, col)) {
                board[row][col] = true;
                count += countNqueens(board, row + 1);
                board[row][col] = false;
            }
        }
        return count;
    }

    public static boolean isitsafetpq(boolean[][] board, int row, int col) {// check
                                                                            // col
        for (int i = row - 1; i >= 0; i--) {
            if (board[i][col]) {
                return false;
            }
        }
        // check diagnol
        for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
            if (board[i][j]) {
                return false;
            }
        }

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

        return true;
    }

}