550B - Preparing Olympiad - CodeForces Solution

#include <bits/stdc++.h>

#define F first
#define S second
#define PB push_back
#define MP make_pair

// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);

typedef long long ll;
typedef long double ld;

using namespace std;

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());


int32_t main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	int n,l,r,x;
	cin >> n >> l >> r >> x;

	vector<int> c(n);
	for (int i = 0; i < n; i++) {
		cin >> c[i];
	}

	int res = 0;
	for (int b = 0; b < (1<<n); b++) {
		vector<int> subset;
		for (int i = 0; i < n; i++) {
			if (b&(1<<i)) subset.PB(c[i]);
		}

		// check if subset verifies conditions
		bool atLeastTwo = (subset.size() >= 2);
		sort(subset.begin(),subset.end());
		bool diffDif = (atLeastTwo && subset[subset.size()-1] - subset[0] >= x);
		bool totalDif;
		int sum = 0;
		for (int i = 0; i < (int)subset.size(); i++) {
			sum += subset[i];
		}
		totalDif = (l <= sum && sum <= r);

		if (atLeastTwo && diffDif && totalDif) res++;
	}
	cout << res << '\n';
}