count the triplets.cpp

/*
///////////////////////////////////////////
//Question/Info

Count the triplets
Easy Accuracy: 42.82% Submissions: 28089 Points: 2
Given an array of distinct integers. The task is to count all the triplets such that sum of two elements equals the third element.

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
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(N2)
Expected Auxiliary Space: O(1)

Constraints:
1 ≤ N ≤ 103
1 ≤ arr[i] ≤ 105

Company Tags
 Amazon Arcesium

author: srj_v
///////////////////////////////////////////
*/

#include <bits/stdc++.h>
using namespace std;

// #define int 		   long long int
#define sbit(x) 	   __builtin_popcount(x)
#define pb(x) 		   push_back(x)
#define mp(x,y) 	   make_pair(x,y)
#define eb(x) 		   emplace_back(x)
#define ct(x) 		   cout << x << "\n";
#define ct2(x,y) 	   cout << x << " " << y << "\n";
#define tc(x) 		   cout << x << " ";
#define tc2(x,y) 	   cout << x << " " << y << " ";
#define forn(i,n) 	   for(int i = 0; i < (int)(n); ++i)
#define forx(i,x,n)    for(int i = x; i < (int)(n); ++i)
#define nfor(i,n)      for(int i = n-1; i >= 0; --i)
#define all(v) 		   v.begin(),v.end()
#define fsp(x,y)       fixed << setprecision(y) << x
#define PI 			   3.1415926535897932384626433832795
#define MOD 		   1000000007 // (1e9+7)
#define pii 		   pair<int,int>
#define pis 		   pair<int,string>
#define vi  		   vector<int>
#define vii 		   vector<pii>
#define mii 		   map<int,int>
#define p_q            priority_queue // priority_queue<int> (&) priority_queue< int,vi,greater<int> >
#define _IOS      	   ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

typedef long double ld;
typedef long long int lli;

#pragma GCC optimize("Ofast")

void c_p_c()
{
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
}


int32_t main() {
///////////
	c_p_c();
///////////
	_IOS
//////////

	// code

	/*
	int t ; cin >> t; while(t--){}
	*/


	class Solution {
	public:

		int countTriplet(int arr[], int n)
		{
			// Your code goes here

			sort(arr, arr + n);

			int count = 0;

			for (int i = n - 1 ; i >= 2 ; --i) {
				// note that i is running till i==2....
				int j = 0 ;
				int k = i - 1;

				while (j < k) {


					if (arr[j] + arr[k] == arr[i]) {
						++count;
						++j; --k;
					}

					else if (arr[j] + arr[k] > arr[i]) {
						--k;
					}
					else {
						++j;
					}
				}

			}
			return count;
		}
	};



// cerr << "time: " << clock() << " ms" << '\n';
	return 0;
}