BZOJ 2300: [HAOI2011]防线修建|set维护凸壳

Posted 2022-11-01 ws_yzy

因为只支持插入操作，所以需要倒过来做..
第一次写维护凸壳的东西…不抄题解..自己YY斜率乱搞（都忘了写叉乘）代码又长常数又大
1A一刻赛艇~
还是找一个靠谱的的模板吧...

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<queue>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#include<iostream>
#define N 500050
#define inf 2000000000
using namespace std;
int sc()

    int i=0,f=1; char c=getchar();
    while(c>'9'||c<'0')if(c=='-')f=-1;c=getchar();
    while(c>='0'&&c<='9')i=i*10+c-'0',c=getchar();
    return i*f;

set<pair<int,int> >st;
double ans,A[100002];
int a[100002],b[100002],d[100002];
int n,fx,fy,top,m,q;
bool c[100002];
double kk(int x,int y)return sqrt((double)x*x+y*y);
double cal(int x,int y)

    if(!x)return inf;
    return (double)y/x;

void add(int x,int y)

    set<pair<int,int> >::iterator it,e;
    it=st.lower_bound(make_pair(x,y));
    if((*it).first==x)return;
    bool flag=0;
    while(++it!=st.end())
    
        pair<int,int> b=*it,a=*--it;
        double l1=cal(a.first-x,a.second-y);
        double l2=cal(b.first-x,b.second-y);
        if(l2<l1)break;
        if(!flag)
        
            pair<int,int> c=*--it;it++;
            ans-=kk(c.first-a.first,c.second-a.second);
            flag=1;
        
        ans-=kk(a.first-b.first,a.second-b.second);
        e=it,++it;
        st.erase(e);
    
    it=st.lower_bound(make_pair(x,y));it--;
    while(it!=st.begin())
    
        pair<int,int> a=*it,b=*--it;
        double l1=cal(a.first-x,a.second-y);
        double l2=cal(b.first-x,b.second-y);
        if(l2>l1)break;
        if(!flag)
        
            it++;it++;
            pair<int,int> c=*it;it--;it--;
            ans-=kk(c.first-a.first,c.second-a.second);
            flag=1;
        
        ans-=kk(a.first-b.first,a.second-b.second);
        e=it,st.erase(++e);
    
    if(flag) 
    
        it=st.lower_bound(make_pair(x,y));
        ans+=kk((*it).first-x,(*it).second-y);
        it--;
        ans+=kk((*it).first-x,(*it).second-y);
        st.insert(make_pair(x,y));
       
    else
    
        it=st.lower_bound(make_pair(x,y));
        pair<int,int> a=*it,b=*--it;
        double l1=cal(a.first-x,a.second-y);
        double l2=cal(b.first-x,b.second-y);
        if(l1<l2)
        
            ans-=kk(a.first-b.first,a.second-b.second);
            ans+=kk((*it).first-x,(*it).second-y);
            it++;
            ans+=kk((*it).first-x,(*it).second-y);
            st.insert(make_pair(x,y));
        
    

int main()

    n=sc(),fx=sc(),fy=sc(),m=sc();
    for(int i=1;i<=m;i++)
        a[i]=sc(),b[i]=sc();
    q=sc();
    for(int i=1;i<=q;i++)
    
        d[i]=sc();
        if(d[i]==1)c[d[i]=sc()]=1;
        else d[i]=0;
    
    st.insert(make_pair(0,0));
    st.insert(make_pair(n,0));
    st.insert(make_pair(fx,fy));
    ans=kk(fx,fy)+kk(fx-n,fy);
    for(int i=1;i<=m;i++)
        if(!c[i])add(a[i],b[i]);
    for(int i=q;i;i--)
    
        if(!d[i])A[++top]=ans;
        else add(a[d[i]],b[d[i]]);
    
    while(top)printf("%.2lf\\n",A[top--]);
    return 0;