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

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

Arnab Chakraborty

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Updated on: 03-Jan-2020

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