# [Solved] Program to Find Pairs that have Desired Sum in Java, Python

Problem Statement: Consider an array of integers that may contain both positive and negative integers, called numbers. Write a program that finds all the pairs of integers whose sum is equal to a given value called the desired sum.

This question has been asked in interviews of many product-based companies like Amazon, Flipkart, Adobe, …

#### Java Program

Prerequisite:

1. Understanding of generics in Java
2. Understanding of ArrayLists in Java
3. Knowledge of classes and objects in Java

Code:

Let’s write a program to find pairs that have desired sum in Java.

```import java.util.*;
class Solution {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
// Enter the size of the array
int n = sc.nextInt();
int[] = arr = new int[n];
for (int i = 0;i < arr.lenght;i++) {
arr[i] = sc.nextInt();
}
// enter the desired sum
int sum = sc.nextInt();
System.out.println(findNumberOfPairs(arr, sum));
}

public static int fndNumberOfPairs(int[] arr, int sum) {
Arrays.sort(arr);  // sort the array
// using two pointer algorithm
int left = 0, right = arr.lenght - 1, count = 0;

while (left < right) {
currentSum = arr[left] + arr[right];
if (currentSum == sum) {
count ++;
left++;
right--;
}
else if (currentSum < sum)
left++;
else
right--;
}
return count;
}
}```

Output:

`Sample Input : n = 5, arr = [1, 2, 3, 4, 5], sum = 4Sample Output : 1 as only (1, 3) pair has the sum equal to 4`

#### Python Program

Now we are implementing the same logic in Python.

Prerequisite:

Code

Let’s write a program to find pairs that have desired sum in Python.

```def count_pair_of_desired_sum(arr, num_sum):
arr.sort()
left = 0
right = len(arr)-1
count = 0
while right > left:
curr_sum = arr[left] + arr[right]

if curr_sum == num_sum:
count += 1
left += 1
right += -1

elif curr_sum > num_sum:
right -= 1

else:
left += 1
return count

out = count_pair_of_desired_sum([1, 3, 2, 6, 7], 9)
print(f"Pair of desired sum: {out}")```

Output:

`Pair of desired sum: 2`

You can use any programming language (C/C++, Java, Python, etc.) of your choice to solve this competitive coding challenge to find pairs that have desired sum.