bzoj1634

分析：经典套路，直接用t/d排序以后直接统计答案就好。

#include<cstdio>
#include<cstring>
#include<algorithm>
#define fo(i,a,b) for(int i=a;i<=b;i++)
#define fd(i,a,b) for(int i=a;i>=b;i--)
using namespace std;
typedef long long ll;
const int N=2e5+5;
int n,m;
struct node
{
    int x,y;
}a[N];
bool cmp(node x,node y)
{
    return x.x*y.y>y.x*x.y;
}
int main()
{
    scanf("%d",&n);
    fo(i,1,n)scanf("%d%d",&a[i].y,&a[i].x);
    sort(a+1,a+1+n,cmp);
    ll ans=0,t=0;
    fo(i,1,n)
    ans+=t*a[i].x,t+=a[i].y*2;
    printf("%lld",ans);
    return 0;
}