SDOI2013 保护出题人

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<cstring>

using namespace std;

struct point{
    double x,y;
    point(double _x=0,double _y=0){
        x=_x;y=_y;
    }
};

point operator +(point a,point b){return point(a.x+b.x,a.y+b.y);}
point operator -(point a,point b){return point(a.x-b.x,a.y-b.y);}
double operator ^(point a,point b){return a.x*b.y-a.y*b.x;}

double xl(point a,point b)
{
    return (b.y-a.y)/(b.x-a.x);
}

point tu[100011],ne;
double tmp,a[100011],x[100011],pre[100011],d;
double ans;
int i,n,t;

double find(point x)
{
    int fn,i,l,r,mid1,mid2;
    double ans1,ans2,ret;
    l=1;
    r=t;
    while(l+2<r){
        fn=(r-l)/3;
        mid1=l+fn;mid2=mid1+fn;
        ans1=xl(tu[mid1],x);ans2=xl(tu[mid2],x);
        if(ans1<ans2)l=mid1+1;
        else r=mid2-1;
    }
    ret=0;
    for(i=l;i<=r;i++)ret=max(ret,xl(tu[i],x));
    return ret;
}

int main()
{
    scanf("%d%lf",&n,&d);
    for(i=1;i<=n;i++){
        scanf("%lf%lf",&a[i],&x[i]);
        pre[i]=pre[i-1]+a[i];
    }
    for(i=1;i<=n;i++){
        ne=point(i*d,pre[i-1]);
        while(t>1&&((tu[t]-tu[t-1])^(ne-tu[t-1]))<0)t--;
        tu[++t]=ne;
        ne=point(x[i]+i*d,pre[i]);
        ans+=find(ne);
    }
    printf("%.0lf\n",ans);
}