bzoj千题计划236：bzoj2300: [HAOI2011]防线修建

Posted 2020-10-24 日拱一卒功不唐捐

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http://www.lydsy.com/JudgeOnline/problem.php?id=2300

维护动态凸包，人懒用的set

用叉积判断，不要用斜率

#include<set>
#include<cmath>
#include<cstdio>
#include<iostream>

using namespace std;

#define N 100001

struct node
{
    int x,y;
    
    node(int x_=0,int y_=0):x(x_),y(y_){}
    
    bool operator < (node p) const
    {
        return x<p.x;
    }
}e[N];

set<node>S;

struct data
{
    int ty,x;
}g[N<<1];

bool cut[N];

double ans;

double Ans[N<<1];
int tot;

void read(int &x)
{
    x=0; char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) { x=x*10+c-‘0‘; c=getchar(); }
}

node operator - (node A,node B) { return node(A.x-B.x,A.y-B.y); }

double Cross(node A,node B) { return A.x*B.y-A.y*B.x; } 

double getdis(node A,node B)
{
    return sqrt((double)(A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));
}

/*double get_slope(node A,node B)
{
    return 1.0*(A.y-B.y)/(A.x-B.x);
}*/

void Insert(node a)
{
    set<node>::iterator it=S.lower_bound(a),l=it,r=it,t;
    l--;
    if(Cross(*r-*l,a-*l)<0) return; 
    ans-=getdis(*r,*l);
    while(1)
    {
        t=r; r++;
        if(r==S.end()) break;
        if(Cross(*r-a,*t-a)<0) ans-=getdis(*t,*r),S.erase(*t);
        else break;
    }
    while(l!=S.begin())
    {
        t=l; l--;
        if(Cross(*t-a,*l-a)<0) ans-=getdis(*t,*l),S.erase(*t);
        else break;
    }
    it=S.upper_bound(a);
    ans+=getdis(a,*it);
    ans+=getdis(a,*(--it));
    S.insert(a);
}

int main()
{
    freopen("defense.in","r",stdin);
    freopen("defense.out","w",stdout); 
    int n,x,y;
    read(n); read(x); read(y);
    S.insert(node(0,0));
    S.insert(node(x,y));
    S.insert(node(n,0));
    ans=getdis(node(0,0),node(x,y))+getdis(node(x,y),node(n,0));
    int m;
    read(m);
    for(int i=1;i<=m;++i) read(e[i].x),read(e[i].y);
    int q;
    read(q);
    for(int i=1;i<=q;++i)
    {
        read(g[i].ty);
        if(g[i].ty==1)
        {
            read(g[i].x);
            cut[g[i].x]=true;
        }
    }
    for(int i=1;i<=m;++i)
        if(!cut[i]) Insert(e[i]);
    for(int i=q;i;--i)
        if(g[i].ty==2) Ans[++tot]=ans;
        else Insert(e[g[i].x]);
    for(int i=tot;i;--i) printf("%.2lf\n",Ans[i]);
    return 0;
}