Count pairs with given sum Java

PROGRAM TO FIND THE NUMBER OF PAIRS OF INTEGERS IN THE ARRAY WHOSE SUM IS EQUAL TO SUM

import java.util.Arrays; 

import java.io.*;

  

class MAIN

{

      

// Function to return the count of pairs

// from arr[] with the given sum

static int pairs_count(int arr[], int n, int sum)

{

    // To store the count of pairs

    int ans = 0;

  

    // Sort the given array

    Arrays.sort(arr);

  

    // Take two pointers

    int i = 0, j = n - 1;

  

    while (i < j)

    {

          

        // If sum is greater

        if (arr[i] + arr[j] < sum)

            i++;

  

        // If sum is lesser

        else if (arr[i] + arr[j] > sum)

            j--;

  

        // If sum is equal

        else 

        {

              

            // Find the frequency of arr[i]

            int x = arr[i], xx = i;

            while ((i < j ) && (arr[i] == x))

                i++;

  

            // Find the frequency of arr[j]

            int y = arr[j], yy = j;

            while ((j >= i )&& (arr[j] == y))

                j--;

  

            // If arr[i] and arr[j] are same

            // then remove the extra number counted

            if (x == y) 

            {

                int temp = i - xx + yy - j - 1;

                ans += (temp * (temp + 1)) / 2;

            }

            else

                ans += (i - xx) * (yy - j);

        }

    }

  

    // Return the required answer

    return ans;

}

  

// Driver code

public static void main (String[] args) 

{

    int arr[] = { 1, 5, 7, 5, -1 };

    int n = arr.length;

    int sum = 6;

      

    System.out.println (pairs_count(arr, n, sum));

}

}







OUTPUT

3

CREDITS: https://www.geeksforgeeks.org/count-pairs-with-given-sum-set-2/