此题题解

话不多说，直接上代码

#include <iostream>
using namespace std;

const int N = 105, M = 2e4 + 5;

int a[N];
bool f[M];

int main() {
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		f[a[i]] = true;
	}
	int ans = 0;
	for (int i = 1; i <= n; i++)
		for (int j = i + 1; j <= n; j++)
			if (f[a[i] + a[j]]) {
				ans++;
				f[a[i] + a[j]] = false;
			}
	cout << ans;
	return 0;
}