割点-模板

Posted 2020-10-26 ckxkexing

洛谷割点模板：https://www.luogu.org/problemnew/show/P3388

#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#include <cstdio>
#include <vector>

using namespace std;
const int maxn = 100009;
vector<int>q,mp[maxn];
int cnt,root,ind;
int num[maxn],low[maxn],used[maxn];
void dfs(int cur,int father)
{
    ind++;
    num[cur]=low[cur]=ind;
    int child=0;
    for(int i=0;i<mp[cur].size();i++)
    {
        int to = mp[cur][i];
        if(num[to]==0)
        {
            child++;
            dfs(to,cur);
            low[cur]=min(low[cur],low[to]);
            //特别注意！有可能在Tarjian时x的儿子有多个！
               //更新时且都符合条件！故ans被累加多次！注意判重！ 
            if(cur!=root&&low[to]>=num[cur])
                if(used[cur]==0)used[cur]=1,cnt++,q.push_back(cur);
            if(root==cur&&child==2)
                if(used[cur]==0)used[cur]=1,cnt++,q.push_back(cur);
        }
        else if(to!=father)
        {
            low[cur]=min(low[cur],num[to]);
        }
    }
}
int main(){
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        int u,v;
        scanf("%d%d",&u,&v);
        mp[u].push_back(v);
        mp[v].push_back(u);
    }
    for(int i=1;i<=n;i++)
    {
        if(num[i]==0)                //由于所有点不是全部连通的；
            ind=0,root=i,dfs(root,0);
    }
    sort(q.begin(),q.end());
    printf("%d\n",cnt);
    for(int i=0;i<q.size();i++)
    {
        printf("%d ",q[i]);
    }
    return 0;
}