T342414 珠心算

首先一眼双指针，写了

喜提10pts

#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
long long n, m;
long long a[N], ans = 0;
int main() {
    cin >> n;
    for (int i = 0; i < n; i ++ ) cin >> a[i];
    for (int i = 0; i < n; i ++) {
    	m = a[i];
	    sort(a, a + n); 
	    int l = 0, r = n - 1;
	    while (l < r) {
	    	while(a[l] + a[r] != m && r > 1) r --;
	    	if (a[l] + a[r] == m) break;
	    	r = n - 1;
	    	l ++;
	    }
	    if (a[l] + a[r] == m) ans ++;
	}
	cout << ans;
    return 0;
}