Count of rooks that can attack each other out of K rooks placed on a N*N chessboard

Given pair of coordinates of K rooks on an N X N chessboard, the task is to count the number of rooks that can attack each other. Note: 1 <= K <= N*N
Examples:

Input: K = 2, arr[][] = { {2, 2}, {2, 3} }, N = 8
Output: 2
Explanation: Both the rooks can attack each other, because they are in the same row. Therefore, count of rooks that can attack each other is 2

Input: K = 1, arr[][] = { {4, 5} }, N = 4
Output: 0

Approach: The task can easily be solved using the fact that, 2 rooks can attack each other if they are either in the same row or in the same column, else they can’t attack each other.

Below is the implementation of the above code:

C++

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to count the number of attacking rooks
int willAttack(vector<vector<int> >& arr, int k, int N)
{
    int ans = 0;

    for (int i = 0; i < k; i++) {
        for (int j = 0; j < k; j++) {

            if (i != j) {

                // Check if rooks are in same row
                // or same column
                if ((arr[i][0] == arr[j][0])
                    || (arr[i][1] == arr[j][1]))
                    ans++;
            }
        }
    }

    return ans;
}

// Driver Code
int main()
{
    vector<vector<int> > arr = { { 2, 2 }, { 2, 3 } };
    int K = 2, N = 8;
    cout << willAttack(arr, K, N);
    return 0;
}

Java

import java.io.*;
import java.util.*;

class Solution {
  static int willAttack(int arr[][], int k, int N)
  {
    int ans = 0;

    for (int i = 0; i < k; i++) {
      for (int j = 0; j < k; j++) {

        if (i != j) {

          // Check if rooks are in same row
          // or same column
          if ((arr[i][0] == arr[j][0])
              || (arr[i][1] == arr[j][1]))
            ans++;
        }
      }
    }

    return ans;
  }

  // Driver code
  public static void main(String[] args)
  {
    int[][] arr = { { 2, 2 }, { 2, 3 } };
    int K = 2, N = 8;
    System.out.println(willAttack(arr, K, N));
  }
}

// This code is contributed by dwivediyash.

Python3

# python program for the above approach

# Function to count the number of attacking rooks
def willAttack(arr, k, N):

    ans = 0

    for i in range(0, k):
        for j in range(0, k):

            if (i != j):

                # Check if rooks are in same row
                # or same column
                if ((arr[i][0] == arr[j][0])
                        or (arr[i][1] == arr[j][1])):
                    ans += 1

    return ans

# Driver Code
if __name__ == "__main__":

    arr = [[2, 2], [2, 3]]
    K = 2
    N = 8
    print(willAttack(arr, K, N))

    # This code is contributed by rakeshsahni

C#

using System;
class Solution
{
  static int willAttack(int[,] arr, int k, int N)
  {
    int ans = 0;

    for (int i = 0; i < k; i++)
    {
      for (int j = 0; j < k; j++)
      {

        if (i != j)
        {

          // Check if rooks are in same row
          // or same column
          if ((arr[i, 0] == arr[j, 0])
              || (arr[i, 1] == arr[j, 1]))
            ans++;
        }
      }
    }

    return ans;
  }

  // Driver code
  public static void Main()
  {
    int[,] arr = { { 2, 2 }, { 2, 3 } };
    int K = 2, N = 8;
    Console.WriteLine(willAttack(arr, K, N));
  }
}

// This code is contributed by gfgking

Javascript

<script>
      // JavaScript code for the above approach

      // Function to count the number of attacking rooks
      function willAttack(arr, k, N) {
          let ans = 0;

          for (let i = 0; i < k; i++) {
              for (let j = 0; j < k; j++) {

                  if (i != j) {

                      // Check if rooks are in same row
                      // or same column
                      if ((arr[i][0] == arr[j][0])
                          || (arr[i][1] == arr[j][1]))
                          ans++;
                  }
              }
          }

          return ans;
      }

      // Driver Code
      let arr = [[2, 2], [2, 3]];
      let K = 2, N = 8;
      document.write(willAttack(arr, K, N));

// This code is contributed by Potta Lokesh
  </script>

Output

2

Time Complexity: O(K*K)
Auxiliary Space: O(1)