https://www.luogu.com.cn/problem/AT_abc194_c

#include <iostream>
using namespace std;
const int MAXX =300001;
int a[MAXX];
long long sum;
int main() {
	int n;
	cin >> n;
	for(int i = 1; i <=n; i ++) {
		cin >> a[i];
	}
	for(int i = 1; i <= n; i ++) {
		for(int j = 1; j <= i - 1; j ++) {
			sum +=(a[i] - a[j]) * (a[i] - a[j]);
		}
	}
	cout<< sum;
}