Count the triplets

Problem Statement - link #

Given an array of distinct integers. The task is to count all the triplets such that sum of two elements equals the third element.

Your Task:

You don’t need to read input or print anything. Your task is to complete the function countTriplet() which takes the array arr[] and N as inputs and returns the triplet count

Expected Time Complexity: O(N^2)
Expected Auxiliary Space: O(1)

Examples #

Example 1:

Input: 
N = 4 
arr[] = {1, 5, 3, 2}
Output: 2 
Explanation: There are 2 triplets:
 1 + 2 = 3 and 3 +2 = 5

Example 2:

Input: 
N = 3
arr[] = {2, 3, 4}
Output: 0
Explanation: No such triplet exits

Constraints #

• 1 ≤ N ≤ 1000
• 1 ≤ arr[i] ≤ 10^5

Solutions #

class Solution{
  public:
	int countTriplet(int arr[], int n)
	{
	    // Your code goes here
	    int res = 0;
	    if(n < 3) {
	        return res;
	    }
	    unordered_set<int> set(arr, arr+n);

	    for(int i = 0; i < n; i++) {
	        for(int j = i + 1; j < n; j++) {
	            if(set.find(arr[i] + arr[j]) != set.end()) {
	                res++;
	            }
	        }
	    }
	    return res;
	}
};