UVA - 796

UVA- 796

/**
          题意：给出一个图，然后看此图的存在的桥，并且输出是哪一个，
          做法：Tarjan（不存在重边）
**/
#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
#include<algorithm>
#include<vector>
using namespace std;
#define maxn 11000
#define maxm 100010
#define INF 0x3f3f3f3f
struct Edge
{
    int to;
    int next;
    bool cut;
} edge[maxm];
int head[maxn],tot;
int Low[maxn],DFN[maxn],Stack[maxn];
int Index,top;
bool Instack[maxn];
bool cut[maxn];
int add_block[maxn];
int bridge;
void addedge(int u,int v)
{
    edge[tot].to = v;
    edge[tot].next = head[u];
    edge[tot].cut = false;
    head[u] = tot++;
}
void Tarjan(int u,int pre)
{
    int v;
    Low[u] = DFN[u] = ++Index;
    Stack[top++] = u;
    Instack[u] = true;
    int son = 0;
    for(int i=head[u]; i != -1; i = edge[i].next)
    {
        v = edge[i].to;
        if(v == pre)
        {
            continue;
        }
        if(!DFN[v])
        {
            son++;
            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;
            }
            ///割点
            if(u!=pre && Low[v] >= DFN[u])
            {
                cut[u] = true;
                add_block[u] ++;
            }
        }
        else if(Low[u] > DFN[v])
        {
            Low[u] = DFN[v];
        }
    }
    if(u == pre && son>1) cut[u] = true;
    if(u == pre)add_block[u] = son -1;
    Instack[u] = false;
    top--;
}
void solve(int N)
{
    memset(DFN,0,sizeof(DFN));
    memset(Instack,false,sizeof(Instack));
    memset(add_block,0,sizeof(add_block));
    memset(cut,false,sizeof(cut));
    Index = top = 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].to > u)
                              {
                                        ans.push_back(make_pair(u,edge[i].to));
                              }
                    }
    }
    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");
}
void Init()
{
          tot = 0;
          memset(head,-1,sizeof(head));
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
#endif // ONLINE_JUDGE
    int n;
    while(~scanf("%d",&n))
    {
        int u,Q,v;
        Init();
        for(int i=1;i<=n;i++)
        {
                              scanf("%d (%d)",&u,&Q);
                              u++;
                              while(Q--)
                              {
                                        scanf("%d",&v);
                                        v++;
                                        if(v<=u) continue;
                                        addedge(u,v);
                                        addedge(v,u);
                              }
        }
        solve(n);

    }
    return 0;
}