# Find pairs in array whose sums already exist in array

• Difficulty Level : Basic
• Last Updated : 14 May, 2021

Given an array of n distinct and positive elements, the task is to find pair whose sum already exists in the given array.
Examples :

```Input : arr[] = {2, 8, 7, 1, 5};
Output : 2 5
7 1

Input : arr[] = {7, 8, 5, 9, 11};
Output : Not Exist```

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

A Naive Approach is to run three loops to find pair whose sum exists in an array.

## C++

 `// A simple C++ program to find pair whose sum``// already exists in array``#include ``using` `namespace` `std;` `// Function to find pair whose sum exists in arr[]``void` `findPair(``int` `arr[], ``int` `n)``{``    ``bool` `found = ``false``;``    ``for` `(``int` `i = 0; i < n; i++) {``        ``for` `(``int` `j = i + 1; j < n; j++) {``            ``for` `(``int` `k = 0; k < n; k++) {``                ``if` `(arr[i] + arr[j] == arr[k]) {``                    ``cout << arr[i] << ``" "` `<< arr[j] << endl;``                    ``found = ``true``;``                ``}``            ``}``        ``}``    ``}` `    ``if` `(found == ``false``)``        ``cout << ``"Not exist"` `<< endl;``}` `// Driven code``int` `main()``{``    ``int` `arr[] = { 10, 4, 8, 13, 5 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``findPair(arr, n);``    ``return` `0;``}`

## Java

 `// A simple Java program to find``// pair whose sum already exists``// in array``import` `java.io.*;` `public` `class` `GFG {` `    ``// Function to find pair whose``    ``// sum exists in arr[]``    ``static` `void` `findPair(``int``[] arr, ``int` `n)``    ``{``        ``boolean` `found = ``false``;``        ``for` `(``int` `i = ``0``; i < n; i++) {``            ``for` `(``int` `j = i + ``1``; j < n; j++) {``                ``for` `(``int` `k = ``0``; k < n; k++) {``                    ``if` `(arr[i] + arr[j] == arr[k]) {``                        ``System.out.println(arr[i] +``                                      ``" "` `+ arr[j]);``                        ``found = ``true``;``                    ``}``                ``}``            ``}``        ``}` `        ``if` `(found == ``false``)``            ``System.out.println(``"Not exist"``);``    ``}` `    ``// Driver code``    ``static` `public` `void` `main(String[] args)``    ``{``        ``int``[] arr = {``10``, ``4``, ``8``, ``13``, ``5``};``        ``int` `n = arr.length;``        ``findPair(arr, n);``    ``}``}` `// This code is contributed by vt_m.`

## Python3

 `# A simple python program to find pair``# whose sum already exists in array` `# Function to find pair whose sum``# exists in arr[]``def` `findPair(arr, n):``    ``found ``=` `False``    ``for` `i ``in` `range``(``0``, n):``        ``for` `j ``in` `range``(i ``+` `1``, n):``            ``for` `k ``in` `range``(``0``, n):``                ``if` `(arr[i] ``+` `arr[j] ``=``=` `arr[k]):``                    ``print``(arr[i], arr[j])``                    ``found ``=` `True` `    ``if` `(found ``=``=` `False``):``        ``print``(``"Not exist"``)` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[ ``10``, ``4``, ``8``, ``13``, ``5` `]``    ``n ``=` `len``(arr)``    ``findPair(arr, n)``    ` `# This code contributed by 29AjayKumar`

## C#

 `// A simple C# program to find``// pair whose sum already exists``// in array``using` `System;` `public` `class` `GFG {` `    ``// Function to find pair whose``    ``// sum exists in arr[]``    ``static` `void` `findPair(``int``[] arr, ``int` `n)``    ``{``        ``bool` `found = ``false``;``        ``for` `(``int` `i = 0; i < n; i++) {``            ``for` `(``int` `j = i + 1; j < n; j++) {``                ``for` `(``int` `k = 0; k < n; k++) {``                    ``if` `(arr[i] + arr[j] == arr[k]) {``                        ``Console.WriteLine(arr[i] +``                                      ``" "` `+ arr[j]);``                        ``found = ``true``;``                    ``}``                ``}``            ``}``        ``}` `        ``if` `(found == ``false``)``            ``Console.WriteLine(``"Not exist"``);``    ``}` `    ``// Driver code``    ``static` `public` `void` `Main(String []args)``    ``{``        ``int``[] arr = {10, 4, 8, 13, 5};``        ``int` `n = arr.Length;``        ``findPair(arr, n);``    ``}``}` `// This code is contributed by vt_m.`

## PHP

 ``

## Javascript

 ``

Output :

`8 5`

An Efficient solution is to store all elements in a hash table (unordered_set in C++) and check one by one all pairs and check its sum exists in set or not. If it exists in the set then print pair. If no pair found in the array then print not exists.

## C++

 `// C++ program to find pair whose sum already``// exists in array``#include ``using` `namespace` `std;` `// Function to find pair whose sum exists in arr[]``void` `findPair(``int` `arr[], ``int` `n)``{``    ``// Hash to store all element of array``    ``unordered_set<``int``> s;``    ``for` `(``int` `i = 0; i < n; i++)``        ``s.insert(arr[i]);` `    ``bool` `found = ``false``;``    ``for` `(``int` `i = 0; i < n; i++) {``        ``for` `(``int` `j = i + 1; j < n; j++) {``            ``// Check sum already exists or not``            ``if` `(s.find(arr[i] + arr[j]) != s.end()) {``                ``cout << arr[i] << ``" "` `<< arr[j] << endl;``                ``found = ``true``;``            ``}``        ``}``    ``}` `    ``if` `(found == ``false``)``        ``cout << ``"Not exist"` `<< endl;``}` `// Driven code``int` `main()``{``    ``int` `arr[] = { 10, 4, 8, 13, 5 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``findPair(arr, n);``    ``return` `0;``}`

## Java

 `// Java program to find pair whose sum``// already exists in array``import` `java.util.*;``import` `java.lang.*;``import` `java.io.*;` `class` `Getpairs {``    ``// Function to find pair whose sum``    ``// exists in arr[]``    ``public` `static` `void` `findPair(``int``[] arr, ``int` `n)``    ``{``        ``/* store all the array elements as a``        ``Hash value*/``        ``HashSet s = ``new` `HashSet();` `        ``for` `(Integer i : arr) {``            ``s.add(i);``        ``}` `        ``/* Run two loop and check for the sum``    ``in the Hashset*/``        ``/* if not a single pair exist then found``    ``will be false else true*/``        ``boolean` `found = ``false``;` `        ``for` `(``int` `i = ``0``; i < n - ``1``; i++) {``            ``for` `(``int` `j = i + ``1``; j < n; j++) {``                ``int` `sum = arr[i] + arr[j];``                ``if` `(s.contains(sum)) {``                    ``/* if the sum is present in``                 ``hashset then found become``                ``true*/``                    ``found = ``true``;` `                    ``System.out.println(arr[i] + ``" "``                                       ``+ arr[j]);``                ``}``            ``}``        ``}` `        ``if` `(found == ``false``)``            ``System.out.println(``"Not Exist "``);``    ``}` `    ``// driver function``    ``public` `static` `void` `main(String args[])``    ``{``        ``int``[] arr = { ``10``, ``4``, ``8``, ``13``, ``5` `};``        ``int` `n = arr.length;``        ``findPair(arr, n);``    ``}``}` `// This code is contributed by Smarak Chopdar`

## Python3

 `# Python3 program to find pair whose``# sum already exist in arrar` `# Function to find pair whose``# sum sxists in arr[]``def` `findPair(arr, n):``    ` `    ``# hash to store all element of array``    ``s ``=` `{i : ``1` `for` `i ``in` `arr}``    ` `    ``found ``=` `False``    ` `    ``for` `i ``in` `range``(n):``        ``for` `j ``in` `range``(i ``+` `1``, n):``            ` `            ``# check if sum already exists or not``            ``if` `arr[i] ``+` `arr[j] ``in` `s.keys():``                ``print``(arr[i], arr[j])``                ``found ``=` `True``    ``if` `found ``=``=` `False``:``        ``print``(``"Not exist"``)``        ` `# Driver code``arr ``=` `[``10``, ``4``, ``8``, ``13``, ``5``]` `n ``=` `len``(arr)` `findPair(arr, n)``    ` `# This code is contributed``# by Mohit Kumar`

## C#

 `// C# program to find pair whose sum``// already exists in array``using` `System;``using` `System.Collections.Generic;` `class` `Getpairs``{``    ``// Function to find pair whose sum``    ``// exists in arr[]``    ``public` `static` `void` `findPair(``int``[] arr, ``int` `n)``    ``{``        ``/* store all the array elements as a``        ``Hash value*/``        ``HashSet<``int``> s = ``new` `HashSet<``int``>();` `        ``foreach` `(``int` `i ``in` `arr)``        ``{``            ``s.Add(i);``        ``}` `        ``/* Run two loop and check for the sum``    ``in the Hashset*/``        ``/* if not a single pair exist then found``    ``will be false else true*/``        ``bool` `found = ``false``;` `        ``for` `(``int` `i = 0; i < n - 1; i++)``        ``{``            ``for` `(``int` `j = i + 1; j < n; j++)``            ``{``                ``int` `sum = arr[i] + arr[j];``                ``if` `(s.Contains(sum))``                ``{``                    ``/* if the sum is present in``                    ``hashset then found become``                    ``true*/``                    ``found = ``true``;` `                    ``Console.WriteLine(arr[i] + ``" "``                                    ``+ arr[j]);``                ``}``            ``}``        ``}` `        ``if` `(found == ``false``)``            ``Console.WriteLine(``"Not Exist "``);``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int``[] arr = { 10, 4, 8, 13, 5 };``        ``int` `n = arr.Length;``        ``findPair(arr, n);``    ``}``}` `// This code contributed by Rajput-Ji`

## Javascript

 ``

Output:

`8 5`

Time Complexity : O(n2)
This article is contributed by DANISH_RAZA. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.