题解 | 不点两面(hard version)

#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main() {
    int m,q ;
    cin>>m>>q;
    set<int>hs;
    map<int,int>mp;
    for(int i=1;i<=q;i++){
        int op,k;
        cin>>op>>k;
        int l=k-3,r=k+3;
        if(op==1){
            if(r<=m)mp[r]++;
            if(l>=0)mp[l]++;
            if(mp[r]==1&&r<=m)hs.insert(r);
            if(mp[l]==1&&l>0)hs.insert(l);
        }else{
            if(r<=m)mp[r]--;
            if(l>=0)mp[l]--;
            if(mp[r]==0&&r<=m)hs.erase(r);
            if(mp[l]==0&&l>0)hs.erase(l);
        }
        cout<<hs.size()<<endl;
    }
}

STL模板库神力