uva796（求桥数目）

#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <queue>
#include <cstdlib>
#include <stack>
#include <vector>
#include <set>
#include <map>
#define LL long long
#define mod 100000000
#define inf 0x3f3f3f3f
#define eps 1e-6
#define N 100010
#define FILL(a,b) (memset(a,b,sizeof(a)))
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define PII pair<int,int>
using namespace std;
struct edge
{
    int v,next;
    edge(){}
    edge(int v,int next):v(v),next(next){}
}e[N<<1];
struct bridge
{
    int u,v;
    bridge(){}
    bridge(int u,int v):u(u),v(v){}
    bool operator<(const bridge &a)const{
        if(u==a.u)return v<a.v;
        return u<a.u;
    }
}b[N<<1];
int n,step,top,tot,num;
int head[N],dfn[N],low[N],Stack[N];
bool instack[N];
map<int,int>mp;
void init()
{
    tot=0;step=0;top=0;num=0;
    FILL(head,-1);FILL(dfn,0);
    FILL(low,0);FILL(instack,false);
    mp.clear();
}
void addedge(int u,int v)
{
    e[tot]=edge(v,head[u]);
    head[u]=tot++;
}
bool isHash(int u,int v)
{
    if(mp[u*N+v])return 1;
    if(mp[v*N+u])return 1;
    mp[u*N+v]=mp[v*N+u]=1;
    return 0;
}
void tarjan(int u,int fa)
{
    dfn[u]=low[u]=++step;
    Stack[top++]=u;
    instack[u]=true;
    for(int i=head[u];~i;i=e[i].next)
    {
        int v=e[i].v;
        if(v==fa)continue;
        if(!dfn[v])
        {
            tarjan(v,u);
            if(low[u]>low[v])low[u]=low[v];
            //桥：一条无向边(u,v)是桥，当且仅当(u,v)为树枝边，且满足DFS[u]<Low[v]
            if(low[v]>dfn[u])
            {
                b[num++]=bridge(min(u,v),max(u,v));
            }
        }
        else if(low[u]>dfn[v])
        {
            low[u]=dfn[v];
        }
    }
    instack[u]=false;
    top--;
}
void solve()
{
    for(int i=1;i<=n;i++)
        if(!dfn[i])tarjan(i,i);
    sort(b,b+num);
    printf("%d critical links\n",num);
    for(int i=0;i<num;i++)
        printf("%d - %d\n",b[i].u,b[i].v);
    puts("");
}
int main()
{
    int u,v;
    while(scanf("%d",&n)>0)
    {
        init();
        for(int i=1;i<=n;i++)
        {
            int t,u,v;
            scanf("%d (%d)",&u,&t);
            while(t--)
            {
                scanf("%d",&v);
                if(!isHash(u,v))
                {
                    addedge(u,v);
                    addedge(v,u);
                }
            }
        }
        solve();
    }
}