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

C++Server Side ProgrammingProgramming

Suppose there is an array of n numbers. We have to find three numbers, such that sum of two elements is same as the third one. So if the array is like [5, 32, 1, 7, 10, 50, 19, 21, 2], the output will be 21, 2, 19. If no such element has found, display that message.

To solve this, we will follow some steps as follows −

• Sort the given array

• Then start fixing the greatest element from the last element and traverse the array to find other two numbers which sum up to the third element.

• Take two pointers j and k, j is from first, k is from last to find the smallest of two numbers from i - 1 to find the largest of the two remaining numbers.

• If the addition of both the numbers is still less than Arr[i], then we have to increase the value of the summation of two numbers, thereby increase the j pointer, so as to increase the value of Arr[j] + Arr[k]

• If the addition of both the numbers is more than Arr[i], then we need to decrease the value of the summation of two numbers, thereby decrease the pointer k, such that decrease the overall value of Arr[j] + Arr[k]

## Example

Live Demo

#include<iostream>
#include<algorithm>
#define N 5
using namespace std;
void getValueTriplet(int arr[], int n) {
sort(arr, arr + n);
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]) {
cout << "The numbers are " << arr[i] << " " << arr[j] << " " << arr[k] << endl;
return;
}
else if (arr[i] > arr[j] + arr[k])
j += 1;
else
k -= 1;
}
}
cout << "No such triplet exists";
}
int main() {
int arr[] = { 5, 32, 1, 7, 10, 50, 19, 21, 2 };
int n = sizeof(arr) / sizeof(arr[0]);
getValueTriplet(arr, n);
}

### Output

The numbers are 21 2 19
Updated on 03-Jan-2020 09:50:15