Uva 796 求桥

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=737

/***
Uva 796 求桥
题目要求：输出题目中所有的桥，按其所连接的点从小到大的顺序输出
解题思路：tarjan算法，所有树枝边都是桥（dfn[u]<low[v]）,利用vector存储一下就可以了
*/
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
const int maxn=10010;
const int maxm=100010;

struct note
{
    int v,next;
    bool cut;
}edge[maxm];

int head[maxn],ip;

void init()
{
    memset(head,-1,sizeof(head));
    ip=0;
}

void addedge(int u,int v)
{
    edge[ip].v=v,edge[ip].next=head[u],edge[ip].cut=false,head[u]=ip++;
}

int dfn[maxn],low[maxn],dex;
int bridge;
int n;

void tarjan(int u,int pre)
{
    dfn[u]=low[u]=++dex;
    for(int i=head[u];i!=-1;i=edge[i].next)
    {
        int v=edge[i].v;
        if(v == pre)continue;
        if(!dfn[v])
        {
            tarjan(v,u);
            if(low[u]>low[v])low[u]=low[v];
            ///桥
            if(low[v]>dfn[u])
            {
                bridge++;
                edge[i].cut=true;
                edge[i^1].cut=true;
            }
        }
        else if(low[u]>dfn[v])
            low[u]=dfn[v];
    }
}

void solve()
{
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    dex=0,bridge=0;
    for(int i=1;i<=n;i++)
    {
        if(!dfn[i])
            tarjan(i,i);
    }
    printf("%d critical links\n",bridge);
    vector<pair<int,int> >ans;
    for(int u=1;u<=n;u++)
    {
        for(int i=head[u];i!=-1;i=edge[i].next)
        {
            if(edge[i].cut&&edge[i].v>u)
            {
                ans.push_back(make_pair(u,edge[i].v));
            }
        }
    }
    sort(ans.begin(),ans.end());
    for(int i=0;i<ans.size();i++)
    {
        printf("%d - %d\n",ans[i].first-1,ans[i].second-1);
    }
    printf("\n");
}

int main()
{
    while(~scanf("%d",&n))
    {
        init();
        for(int i=0;i<n;i++)
        {
            int u,num;
            scanf("%d (%d)",&u,&num);
            u++;
            while(num--)
            {
                int v;
                scanf("%d",&v);
                v++;
                if(v<=u)continue;
                addedge(u,v);
                addedge(v,u);
            }
        }
        solve();
    }
    return 0;
}