tarjan进阶

//割点
void tarjan(int u){
    int fl=0;
    dfn[u]=low[u]=++cnt;
    for(int i=hed[u];i;i=nxt[i]){
        int v=ver[i];
        if(!dfn[v]){
            tarjan(v);
            low[u]=min(low[u],low[v]);
            if(low[v]>=dfn[u]){
                fl++;
                if(fl>1||u!=root){
                    cut[u]=1;
                }
            }
        }
        else{
            low[u]=min(low[u],dfn[v]);
        }
    }
}

//割边 
void tarjan(int u,int in_edg){
    dfn[u]=low[u]=++cnt;
    for(int i=hed[u];i;i=nxt[i]){
        int v=ver[i];
        if(!dfn[v]){
            tarjan(v,i);
            low[u]=min(low[u],low[v]);
            if(dfn[u]<low[v]){
                bridge[i]=bridge[i^1]=1;
            }
        }
        else if(i!=(in_edg^1)){
            low[u]=min(low[u],dfn[v]);
        }
    }
}

//点双缩点 
void tarjan(int x){
    dfn[x]=low[x]=++cnt;
    ins[x]=1;
    s.push(x);
    if(!siz[x]){
        dcc[++cntt].push_back(x);
        return ;
    }
    int ch=0;
    for(int i=hed[x];i;i=nxt[i]){
        int y=ver[i];
        if(!dfn[y]){
            tarjan(y);
            low[x]=min(low[x],low[y]);
            if(low[y]>=dfn[x]){
                ch++;
                if(rt!=x||ch>1){
                    cut[x]=1;
                }
                cntt++;
                int z;
                do{
                    z=s.top();
                    ins[z]=0;
                    s.pop();
                    dcc[cntt].push_back(z);
                }while(y!=z);
                dcc[cntt].push_back(x);
            }
        }
        else{
            low[x]=min(low[x],dfn[y]);
        }
    }
}
num=cnt;
for(int i=1;i<=n;i++){
    if(cut[i]){
        new_id[i]=++num;
    }
}
tc=1;
for(int i=1;i<=cnt;i++){
    for(int j=0;j<dcc[i].size();j++){
        int x=dcc[i][j];
        if(cut[x]){
            add_c(i,new_id[x]);
            add_c(new_id[x],i);
        }
    }
}

//边双缩点 
void tarjan(int u,int in_edg){
    dfn[u]=low[u]=++cnt;
    for(int i=hed[u];i;i=nxt[i]){
        int v=ver[i];
        if(!dfn[v]){
            tarjan(v,i);
            low[u]=min(low[u],low[v]);
            if(low[v]>dfn[u]){
                brg[i]=brg[i^1]=1;
            }
        }
        else if(i!=(in_edg^1)){
            low[u]=min(low[u],dfn[v]);
        }
    }
}
void dfs(int u){
    vis[u]=1;
    stk[ans].push_back(u);
    for(int i=hed[u];i;i=nxt[i]){
        int v=ver[i];
        if(brg[i]||vis[v]){
            continue;
        }
        dfs(v);
    }
}
 
//SCC 
void tarjan(int u){
    low[u]=dfn[u]=++cnt;
    s.push(u),ins[u]=1;
    for(int i=hed[u];i;i=nxt[i]){
        int v=ver[i];
        if(!dfn[v]){
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(ins[u]){
            low[u]=min(low[u],dfn[v]);
        }
    }
    if(dfn[u]==low[u]){
        k++;
        do{
            t=s.top();
            s.pop();
            ins[t]=0;
            blgscc[t]=k;
            smscc[k]++;
        }while(t!=u);
    }
}