four different.cpp

// Find four different elements a,b,c and d of array such that
// a+b = c+d
#include<bits/stdc++.h>
using namespace std;

bool findPairs(int arr[], int n)
{
	// Create an empty Hash to store mapping from sum to
	// pair indexes
	map<int, pair<int, int> > Hash;

	// Traverse through all possible pairs of arr[]
	for (int i = 0; i < n; ++i)
	{
		for (int j = i + 1; j < n; ++j)
		{
			// If sum of current pair is not in hash,
			// then store it and continue to next pair
			int sum = arr[i] + arr[j];
			if (Hash.find(sum) == Hash.end())
				Hash[sum] = make_pair(i, j);

			else // Else (Sum already present in hash)
			{
				// Find previous pair
				pair<int, int> pp = Hash[sum];// pp->previous pair

				// Since array elements are distinct, we don't
				// need to check if any element is common among pairs
				cout << "(" << arr[pp.first] << ", " << arr[pp.second]
					<< ") and (" << arr[i] << ", " << arr[j] << ")n";
				return true;
			}
		}
	}

	cout << "No pairs found";
	return false;
}

// Driver program
int main()
{
	int arr[] = {3, 4, 7, 1, 2, 9, 8};
	int n = sizeof arr / sizeof arr[0];
	findPairs(arr, n);
	return 0;
}