Gym 100801G Graph 拓扑排序

Posted 2020-08-04

http://codeforces.com/gym/100801/attachments

用set维护一下入度为零的点，每次将当前指针和下一个指针连一条边

写博客只是为了纪念一下第一次用set，还有我逝去的4小时青春

PS.iterator在迭代器中不要xjb改

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<queue>
#include<set>
using namespace std;
int n,m,k;
set<int>s;
int f[200000],g[200000];
int sum[200000],tot,sedge;
struct point 
{
    int to,next;
}e[10000000];
void add(int x,int y)
{
    e[++tot].to=y;
    e[tot].next=g[x];
    g[x]=tot;
}
int main()
{
    freopen("graph.in","r",stdin);
    freopen("graph.out","w",stdout);
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=m;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        add(x,y);
        sum[y]++;
    }
    for(int i=1;i<=n;i++)
    {
        if(sum[i]==0)
        s.insert(i);
    }//cout<<"!!!!!!"<<endl;
    int sk=k;
    for(int p=1;p<=n;p++)
    {
        int flag=1;
        set<int>::iterator itlast=s.end();itlast--;//cout<<"!!!!!!"<<endl;
        set<int>::iterator itar;
        //cout<<*itlast<<endl;
        for(set<int>::iterator it=s.begin();it!=itlast;it++)
        {//cout<<"!!!!!!"<<endl;
            //cout<<*it<<endl;
            if(f[*it])
            {
                set<int>::iterator tmp=it;
                tmp++;
                f[*it]=*tmp;
                add(*tmp,*it);
                sum[*it]++;
                continue;
            }
            if(f[*it]==0&&sk>0)
            {
                set<int>::iterator tmp=it;
                tmp++;
                f[*it]=*tmp;
                //cout<<*tmp<<" "<<*it<<endl;
                add(*tmp,*it);
                sum[*it]++;//cout<<"!!!!!!"<<endl;
                sk--;
                continue;
            }
            printf("%d ",*it);
            itar=it;
            flag=0;
            break;
        }
        if(flag)
        {
            set<int>::iterator itlast=s.end();itlast--;
            printf("%d ",*itlast);
            int x=*itlast;
            s.erase(s.begin(),s.find(x));
            s.erase(x);
            for(int temp=g[x];temp;temp=e[temp].next)
            {
                sum[e[temp].to]--;
                if(sum[e[temp].to]==0)
                s.insert(e[temp].to);
            }
        }
        else
        {
            int x=*itar;
            s.erase(s.begin(),s.find(x));
            s.erase(x);
            for(int temp=g[x];temp;temp=e[temp].next)
            {
                sum[e[temp].to]--;
                if(sum[e[temp].to]==0)
                s.insert(e[temp].to);
            }
        }
    }
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        if(f[i])ans++;
    }
    cout<<endl<<ans<<endl;
    for(int i=1;i<=n;i++)
    if(f[i])printf("%d %d\n",f[i],i);
    return 0;
}