3203: [Sdoi2013]保护出题人 凸包+三分

膜IOI爷的题解
凸包上三分。。

#include<iostream>#include<cstdio>#define N 100105using namespace std;int n,top,stack[N];double d;double sum[N],x[N];struct node {double x,y;} a[N];double cross(node a,node b,node c){    return (a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y);}double slop(node a,node b){    return (a.y-b.y)/(a.x-b.x);}double find(node t){    int l=1,r=top,lmid,rmid;    while (r-l>=3)    {        lmid=l+(r-l)/3;        rmid=r-(r-l)/3;        double K1=slop(a[stack[lmid]],t),K2=slop(a[stack[rmid]],t);        if (K1<K2) l=lmid; else r=rmid;    }    double ans=0.0;    for (int i=l;i<=r;i++) ans=max(ans,slop(a[stack[i]],t));    return ans;}int main(){    scanf("%d%lf",&n,&d);    for (int i=1;i<=n;i++)    {        scanf("%lf%lf",&sum[i],&x[i]);        sum[i]+=sum[i-1];         a[i]=(node){i*d,sum[i-1]};    }    double ans=0;    for (int i=1;i<=n;i++)    {        while (top>1&&cross(a[i],a[stack[top]],a[stack[top-1]])>=0) top--;        stack[++top]=i;        node q=(node){x[i]+i*d,sum[i]};        ans+=find(q);    }    printf("%.0lf\n",ans);    return 0;}