![\sum_{i=1}^{n}\sum \sum_{j=i+1}^{n}max(a[j]-a[i],0)](https://latex.csdn.net/eq?%5Csum_%7Bi%3D1%7D%5E%7Bn%7D%5Csum%20%5Csum_%7Bj%3Di+1%7D%5E%7Bn%7Dmax%28a%5Bj%5D-a%5Bi%5D%2C0%29)
=![\sum_{i=1}^{n}(i-1)a[i]](https://latex.csdn.net/eq?%5Csum_%7Bi%3D1%7D%5E%7Bn%7D%28i-1%29a%5Bi%5D)
减![\sum_{i=1}^{n}\sum_{j=i+1}^{n}max(-a[i],-a[j])](https://latex.csdn.net/eq?%5Csum_%7Bi%3D1%7D%5E%7Bn%7D%5Csum_%7Bj%3Di+1%7D%5E%7Bn%7Dmax%28-a%5Bi%5D%2C-a%5Bj%5D%29)
sort拍后就A了
#include <bits/stdc++.h>
#include <cstring>
using namespace std;
typedef long long ll;
ll n,a[400005],cnt=0,b[400005];
bool cmp(long long x,long long y){
return x>y;
}
int main () {
cin>>n;
for(int i=1;i<=n;i++){
cin>>a[i];
cnt+=a[i]*(i-1);
}
sort(a+1,a+1+n,cmp);
for(int i=1;i<=n;i++){
cnt-=(i-1)*a[i];
}
cout<<cnt;
return 0;
}
