bzoj千题计划237：bzoj1492: [NOI2007]货币兑换Cash

#include<cmath>
#include<cstdio>
#include<algorithm>
#include<iostream>

using namespace std;

#define N 100001

const double eps=1e-7;

struct node
{
    double A,B,R;
    double X,Y;
    double K;
    int id;
    
    bool operator < (node p) const
    {
        /*if(fabs(X-p.X)>eps)  return X<p.X;
        return Y<p.Y;*/
        return X<p.X;
    }
    
}e[N],t[N]; 

double dp[N],ans;

int st[N],top;

bool down(int i,int j,int k)
{
    return (e[j].X-e[i].X)*(e[k].Y-e[i].Y)-(e[k].X-e[i].X)*(e[j].Y-e[i].Y)<0;
}

void solve(int l,int r)
{
    if(l==r)
    {
        dp[l]=max(dp[l],dp[l-1]);
        e[l].Y=dp[l]/(e[l].A*e[l].R+e[l].B);
        e[l].X=e[l].Y*e[l].R;
        return;
    }
    int mid=l+r>>1;
    int opl=l,opr=mid+1;
    for(int i=l;i<=r;++i)
        if(e[i].id<=mid) t[opl++]=e[i];
        else t[opr++]=e[i];
    for(int i=l;i<=r;++i) e[i]=t[i];
    solve(l,mid);
    top=0;
    for(int i=l;i<=mid;++i)
    {
        while(top>1 && !down(st[top-1],st[top],i)) top--;
        st[++top]=i;
    }
    int now=1;
    for(int i=mid+1;i<=r;++i)
    {
        while(now<top && (e[st[now]].Y-e[st[now+1]].Y)<(e[st[now]].X-e[st[now+1]].X)*e[i].K) now++;
        dp[e[i].id]=max(dp[e[i].id],e[st[now]].X*e[i].A+e[st[now]].Y*e[i].B);
    }
    solve(mid+1,r);
    opl=l; opr=mid+1;
    for(int i=l;i<=r;++i) 
        if(opl>mid) t[i]=e[opr++];
        else if(opr>r) t[i]=e[opl++];
        else if(e[opl]<e[opr]) t[i]=e[opl++];
        else t[i]=e[opr++];
    for(int i=l;i<=r;++i) e[i]=t[i];
}        

bool cmp(node p,node q)
{
    return p.K>q.K;
}

int main()
{
    int n;
    double m;
    scanf("%d%lf",&n,&dp[0]);
    for(int i=1;i<=n;++i) 
    {
        scanf("%lf%lf%lf",&e[i].A,&e[i].B,&e[i].R);
        e[i].K=-e[i].A/e[i].B;
        e[i].id=i;
    }
    sort(e+1,e+n+1,cmp);
    solve(1,n);
    printf("%.3lf",dp[n]);
}