kuangbin专题 专题九 连通图 Network UVA

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 = 110;
int n,tim,tot,root = 1;
int head[N],dfn[N],low[N],poi[N];
struct node{
    int to;
    int nxt;
}e[N*N];

void init(){
    for(int i = 0; i <= n; ++i){
        head[i] = -1;
        dfn[i] = poi[i] = 0;
    }
    tim = tot = 0;
}

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 = 0;
    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] = 1;
        }
        else if(low[now] > dfn[to]) low[now] = dfn[to];
    }
    //割点条件2
    if(now == root && son >= 2) poi[now] = 1;
}

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 == '
') break;
            }
        }
        tarjan(1,1);
        int ans = 0;
        for(int i = 0; i <= n; ++i)
            if(poi[i]) ++ans;

        printf("%d
",ans);
    }


    return 0;
}