Cp0d8Y - Online C++0x Compiler & Debugging Tool

#include <iostream>
#include<bits/stdc++.h>

using namespace std;

int lessthank(vector<int> &nums,int k){
	int i=0;
	int j = nums.size()-1;
	int ans=0;

	while(i<j){
		int sum = nums[i]+nums[j];

		if(sum<=k){
			ans = ans + (j-i);
			i++;
		}
		j--;
	}

	return ans;

}

int main() {
	// your code goes here
	int n,l,r;
	cin>>n>>l>>r;
	vector<int> nums(n);
	for(int i=0;i<n;i++){
		cin>>nums[i];
	}

	sort(nums.begin(),nums.end());
	int fr = lessthank(nums,r);
	int fl = lessthank(nums,l-1);
	cout<<fr-fl<<endl;


	return 0;
}