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

2 Comments
Sachin Sharma
Updated: Jun 28, 2022

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.

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Java Program

Prerequisite:

Understanding of generics in Java
Understanding of ArrayLists in Java
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 = 4
Sample 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:

You can use either sort() or sorted() method to sort the Python list array.

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.

Sachin Sharma

I am Sachin Sharma a complete JAVA geek and I also have good knowledge of Python, C, C++, and front-end development. I am a 5-star gold coder on Hckerrank in JAVA, Python, C++, and DSA. I am eager to share my coding knowledge to help people.

2 Comments

parth says:

March 28, 2022 at 1:37 pm

currentSum = arr[left] + arr[right]; this line should be inside the while loop.

Reply
1. Aniruddha Chaudhari says:
  
  June 28, 2022 at 9:03 am
  
  Thanks for notifying the correction, Parth. Fixed.
  
  Reply