题解 | #数的选择#

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
	int n;
	cin >> n;
	vector<long long> a(n);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	int ans = -1;
	sort(a.begin(), a.end());
	vector<long long> prefix_sum = { 0 };
	for (int i = 0; i < n; i++) {
		prefix_sum.push_back(prefix_sum.back() + a[i]);
	}
	vector<long long> suffix_sums = { 0 };
	for (int i = n - 1; i >= 0; i--) {
		suffix_sums.push_back(suffix_sums.back() + a[i]);
	}
	for (int k = 1; k <=n; k++) {
		if (2 * k + 1 <= n) {
			long long b = prefix_sum[k + 1];
			long long r = suffix_sums[k];
			if (b < r) {
				ans = k;
				break;
			}
		}
	}
	cout << ans << endl;
	return 0;
}