백준 1253 좋다

백준 1253

#include <bits/stdc++.h>
using namespace std;
int n;
int arr[2001], vis[2001];
int main() {
	ios::sync_with_stdio(0); cin.tie(0);

	cin >> n;

	for (int i = 0; i < n; i++) cin >> arr[i];

	sort(arr, arr + n);

	int flag = 0;
	for (auto c : arr) {
		if (c) flag = 1;
	}

	int cnt = 0;
	if (flag) {
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {

				if (i == j) continue;

				int idx = lower_bound(arr, arr + n, arr[i] - arr[j]) - arr;

				if (idx == i || idx == j) continue;

				if (arr[j] + arr[idx] == arr[i]) {
					cnt++;
					break;
				}

			}
		}
		cout << cnt << '\n';
	}
	else {
		cout << n << '\n';
	}
}