學的指標寫法 /se

需要轉換一下，就變成了線段問題，然後1，2的兩種情況分別也是對應+-的斜率qwq

《維護凸》

#include<bits/stdc++.h>

#define int long long
using namespace std;


int n;
struct node
{
    int x,y;
    bool operator < (node T) const
    {
        return x==T.x?y>T.y:x<T.x;
    }
    node operator - (node T) const
    {
        
 
return {x-T.x,y-T.y};
    }
    int operator ^ (node T) const
    {
        return x*T.y - y*T.x;
    }
};

struct Hull : public multiset<node>
{
    bool inside(iterator p)
    {
        auto t2=next(p);
        if(t2==end())
        return 0;
        if(p==begin())
        return t2->x > p->x && t2->y > p->y;
        auto t1
 
=prev(p);
        if(((*t1-*p)^(*t2-*p)) < 0)
        return 1;
        else
        return 0;
    }
    
    void ins(node p)
    {
        auto t=insert(p);
        if(inside(t))
        {
            erase(t);
            return ;
        }
        while(t!=begin() &&inside(prev(t)))
        erase(prev(t));
        
 
while(next(t)!=end() &&inside(next(t)))
        erase(next(t));
    }
    
};


signed main()
{
    ios::sync_with_stdio(false);
    cin>>n;
     
    Hull hull; 
     
    for(int i=1;i<=n;i++) 
    {
        int x,y;
        cin>>x>>y;
        node t={x,y};        
        hull.ins(t);
        
        cout<<i-hull.size()<<endl;
    }
    return 0;
}