kuangbin专题 专题九 连通图 Network UVA - 315

题目链接：https://vjudge.net/problem/UVA-315

题目：求割点。

 #include <iostream>
 #include <cstdio>
 #include <algorithm>
 using namespace std;

 const int N = ;
 int n,tim,tot,root = ;
 int head[N],dfn[N],low[N],poi[N];
 struct node{
     int to;
     int nxt;
 }e[N*N];

 void init(){
     for(int i = ; i <= n; ++i){
         head[i] = -;
         dfn[i] = poi[i] = ;
     }
     tim = tot = ;
 }

 inline void add(int u,int v){
     e[tot].to = v;
     e[tot].nxt = head[u];
     head[u] = tot++;
 }

 void tarjan(int now,int pre){
     dfn[now] = low[now] = ++tim;
     int to,son = ;
     for(int o = head[now]; ~o; o = e[o].nxt){
         to = e[o].to;
         if(to == pre) continue; //处理无向图的双向边问题
         if(!dfn[to]){
             ++son;
             tarjan(to,now);
             low[now] = min(low[now],low[to]);
             //割点条件1
             if(now != root && dfn[now] <= low[to]) poi[now] = ;
         }
         else if(low[now] > dfn[to]) low[now] = dfn[to];
     }
     //割点条件2
     if(now == root && son >= ) poi[now] = ;
 }

 int main(){

     int u,v;
     char ch;

     while(~scanf("%d",&n) && n){
         init();

         while(~scanf("%d",&u) && u){
             while(~scanf("%d%c",&v,&ch)){
                 add(u,v); add(v,u);
                 if(ch == '\n') break;
             }
         }
         tarjan(,);
         int ans = ;
         for(int i = ; i <= n; ++i)
             if(poi[i]) ++ans;

         printf("%d\n",ans);
     }

     return ;
 }