# Find a triplet such that sum of two equals to third element

Given an array of integers you have to find three numbers such that sum of two elements equals the third element.

Examples:

```Input : {5, 32, 1, 7, 10, 50, 19, 21, 2}
Output : 21, 2, 19

Input : {5, 32, 1, 7, 10, 50, 19, 21, 0}
Output : no such triplet exist
```

Question source : Arcesium Interview Experience | Set 7 (On campus for Internship)

## Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

Simple approach: Run three loops and check if there exists a triplet such that sum of two elements equals the third element.

Time complexity: O(n^3)

Efficient approach : The idea is similar to Find a triplet that sum to a given value.

• Sort the given array first.
• Start fixing the greatest element of three from back and traverse the array to find other two numbers which sum upto the third element.
• Take two pointers j(from front) and k(initially i-1) to find the smallest of the two number and from i-1 to find the largest of the two remaining numbers
• If the addition of both the numbers is still less than A[i], then we need to increase the value of the summation of two numbers, thereby increase the j pointer, so as to increase the value of A[j] + A[k].
• If the addition of both the numbers is more than A[i], then we need to decrease the value of the summation of two numbers, thereby decrease the k pointer so as to decrease the overall value of A[j] + A[k].

Below image is a dry run of the above approach: Below is the implementation of the above approach:

## C++

 `// CPP program to find three numbers ` `// such that sum of two makes the ` `// third element in array ` `#include ` `using` `namespace` `std; ` ` `  `// Utility function for finding ` `// triplet in array ` `void` `findTriplet(``int` `arr[], ``int` `n) ` `{ ` `    ``// sort the array ` `    ``sort(arr, arr + n); ` ` `  `    ``// for every element in arr ` `    ``// check if a pair exist(in array) whose ` `    ``// sum is equal to arr element ` `    ``for` `(``int` `i = n - 1; i >= 0; i--) { ` `        ``int` `j = 0; ` `        ``int` `k = i - 1; ` ` `  `        ``// Iterate forward and backward to find ` `        ``// the other two elements ` `        ``while` `(j < k) { ` ` `  `            ``// If the two elements sum is ` `            ``// equal to the third element ` `            ``if` `(arr[i] == arr[j] + arr[k]) { ` ` `  `                ``// pair found ` `                ``cout << ``"numbers are "` `<< arr[i] << ``" "` `                     ``<< arr[j] << ``" "` `<< arr[k] << endl; ` `                ``return``; ` `            ``} ` ` `  `            ``// If the element is greater than ` `            ``// sum of both the elements, then try ` `            ``// adding a smaller number to reach the ` `            ``// equality ` `            ``else` `if` `(arr[i] > arr[j] + arr[k]) ` `                ``j += 1; ` ` `  `            ``// If the element is smaller, then ` `            ``// try with a smaller number ` `            ``// to reach equality, so decrease K ` `            ``else` `                ``k -= 1; ` `        ``} ` `    ``} ` ` `  `    ``// No such triplet is found in array ` `    ``cout << ``"No such triplet exists"``; ` `} ` ` `  `// driver program ` `int` `main() ` `{ ` `    ``int` `arr[] = { 5, 32, 1, 7, 10, 50, 19, 21, 2 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` ` `  `    ``findTriplet(arr, n); ` `    ``return` `0; ` `} `

## Java

 `// Java program to find three numbers ` `// such that sum of two makes the ` `// third element in array ` `import` `java.util.Arrays; ` ` `  `public` `class` `GFG { ` ` `  `    ``// utility function for finding ` `    ``// triplet in array ` `    ``static` `void` `findTriplet(``int` `arr[], ``int` `n) ` `    ``{ ` `        ``// sort the array ` `        ``Arrays.sort(arr); ` ` `  `        ``// for every element in arr ` `        ``// check if a pair exist(in array) whose ` `        ``// sum is equal to arr element ` `        ``for` `(``int` `i = n - ``1``; i >= ``0``; i--) { ` `            ``int` `j = ``0``; ` `            ``int` `k = i - ``1``; ` `            ``while` `(j < k) { ` `                ``if` `(arr[i] == arr[j] + arr[k]) { ` ` `  `                    ``// pair found ` `                    ``System.out.println(``"numbers are "` `+ arr[i] + ``" "` `                                       ``+ arr[j] + ``" "` `+ arr[k]); ` ` `  `                    ``return``; ` `                ``} ` `                ``else` `if` `(arr[i] > arr[j] + arr[k]) ` `                    ``j += ``1``; ` `                ``else` `                    ``k -= ``1``; ` `            ``} ` `        ``} ` ` `  `        ``// no such triplet is found in array ` `        ``System.out.println(``"No such triplet exists"``); ` `    ``} ` ` `  `    ``// driver program ` `    ``public` `static` `void` `main(String args[]) ` `    ``{ ` `        ``int` `arr[] = { ``5``, ``32``, ``1``, ``7``, ``10``, ``50``, ``19``, ``21``, ``2` `}; ` `        ``int` `n = arr.length; ` `        ``findTriplet(arr, n); ` `    ``} ` `} ` `// This code is contributed by Sumit Ghosh `

## Python

 `# Python program to find three numbers ` `# such that sum of two makes the ` `# third element in array ` ` `  `# utility function for finding ` `# triplet in array ` `def` `findTriplet(arr, n): ` `     `  `    ``# sort the array ` `    ``arr.sort() ` `  `  `    ``# for every element in arr ` `    ``# check if a pair exist(in array) whose ` `    ``# sum is equal to arr element ` `    ``i ``=` `n ``-` `1` `    ``while``(i >``=` `0``): ` `        ``j ``=` `0` `        ``k ``=` `i ``-` `1` `        ``while` `(j < k): ` `            ``if` `(arr[i] ``=``=` `arr[j] ``+` `arr[k]): ` `                `  `                ``# pair found ` `                ``print` `"numbers are "``, arr[i], arr[j], arr[k] ` `                ``return` `            ``elif` `(arr[i] > arr[j] ``+` `arr[k]): ` `                ``j ``+``=` `1` `            ``else``: ` `                ``k ``-``=` `1` `        ``i ``-``=` `1` `         `  `    ``# no such triplet is found in array ` `    ``print` `"No such triplet exists"` `  `  `# driver program ` `arr ``=` `[ ``5``, ``32``, ``1``, ``7``, ``10``, ``50``, ``19``, ``21``, ``2` `] ` `n ``=` `len``(arr) ` `findTriplet(arr, n) ` ` `  `# This code is contributed by Sachin Bisht `

## C#

 `// C# program to find three numbers ` `// such that sum of two makes the ` `// third element in array ` `using` `System; ` ` `  `public` `class` `GFG { ` ` `  `    ``// utility function for finding ` `    ``// triplet in array ` `    ``static` `void` `findTriplet(``int``[] arr, ``int` `n) ` `    ``{ ` ` `  `        ``// sort the array ` `        ``Array.Sort(arr); ` ` `  `        ``// for every element in arr ` `        ``// check if a pair exist(in ` `        ``// array) whose sum is equal ` `        ``// to arr element ` `        ``for` `(``int` `i = n - 1; i >= 0; i--) { ` `            ``int` `j = 0; ` `            ``int` `k = i - 1; ` `            ``while` `(j < k) { ` `                ``if` `(arr[i] == arr[j] + arr[k]) { ` ` `  `                    ``// pair found ` `                    ``Console.WriteLine(``"numbers are "` `                                      ``+ arr[i] + ``" "` `+ arr[j] ` `                                      ``+ ``" "` `+ arr[k]); ` ` `  `                    ``return``; ` `                ``} ` `                ``else` `if` `(arr[i] > arr[j] + arr[k]) ` `                    ``j += 1; ` `                ``else` `                    ``k -= 1; ` `            ``} ` `        ``} ` ` `  `        ``// no such triplet is found in array ` `        ``Console.WriteLine(``"No such triplet exists"``); ` `    ``} ` ` `  `    ``// driver program ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``int``[] arr = { 5, 32, 1, 7, 10, 50, ` `                      ``19, 21, 2 }; ` `        ``int` `n = arr.Length; ` ` `  `        ``findTriplet(arr, n); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m. `

## PHP

 `= 0; ``\$i``--) ` `    ``{ ` `        ``\$j` `= 0; ` `        ``\$k` `= ``\$i` `- 1; ` `        ``while` `(``\$j` `< ``\$k``)  ` `        ``{ ` `            ``if` `(``\$arr``[``\$i``] == ``\$arr``[``\$j``] + ``\$arr``[``\$k``])  ` `            ``{ ` `                 `  `                ``// pair found ` `                ``echo` `"numbers are "``, ``\$arr``[``\$i``], ``" "``,  ` `                                      ``\$arr``[``\$j``], ``" "``,  ` `                                      ``\$arr``[``\$k``]; ` `                ``return``; ` `            ``}  ` `            ``else` `if` `(``\$arr``[``\$i``] > ``\$arr``[``\$j``] +  ` `                                ``\$arr``[``\$k``]) ` `                ``\$j` `+= 1; ` `            ``else` `                ``\$k` `-= 1; ` `        ``} ` `    ``} ` ` `  `    ``// no such triplet  ` `    ``// is found in array ` `    ``echo` `"No such triplet exists"``; ` `} ` ` `  `// Driver Code ` `\$arr` `= ``array``(5, 32, 1, 7, 10,  ` `             ``50, 19, 21, 2 ); ` `\$n` `= ``count``(``\$arr``); ` ` `  `findTriplet(``\$arr``, ``\$n``); ` ` `  `// This code is contributed by anuj_67. ` `?> `

Output:

```numbers are 21 2 19
```

Time complexity: O(N^2)

This article is contributed by Mandeep Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.