暴力时间复杂度为O(n^2),推公式时间复杂度为O(n)
#include <iostream>
#include <cstring>
#include <algorithm>
#define MAXN 100010
using namespace std;
typedef long long LL;
int x[MAXN],y[MAXN];
LL res=0;
int main()
{
int n;
scanf("%d",&n);
LL sum1=0,sum2=0;
for(int i=1;i<=n;i++)
{
scanf("%d %d",&x[i],&y[i]);
sum1+=x[i];
sum2+=y[i];
}
for(int i=1;i<=n;i++)
res+=(x[i]*x[i]+y[i]*y[i]);
res*=n;
res-=sum1*sum1+sum2*sum2;
printf("%lld\n",res);
return 0;
}