牛客寒假算法基础集训营3 D. 处女座的训练(思维)

#include <bits/stdc++.h>
#define ll long long
using namespace std;
int n;
struct Node{
  ll x,y;
}Edge[100005];

bool cmp(Node a, Node b){
  return a.y * b.x > b.y * a.x;
}

int main()
{
  scanf("%d",&n);
  ll sum = 0;
  for(int i=0;i<n;i++){
    scanf("%lld%lld",&Edge[i].x,&Edge[i].y);
    sum += Edge[i].y;
  }
  sort(Edge, Edge + n, cmp);
  ll ans = 0;
  for(int i=0;i<n;i++){
    sum -= Edge[i].y;
    ans += Edge[i].x * sum;
  }
  printf("%lld\n",ans);
  return 0;
}