uva 796

传送门；https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=737

解题思路：

就是一个简单的求割边问题。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <algorithm>
using namespace std;

const int MAXN=10010;
const int MAXM=100100;

struct Edge{
    int to,next;
    bool cut;
}edge[MAXM];

int head[MAXN],tot;

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

void addEdge(int u,int v){
    edge[tot].to=v;
    edge[tot].next=head[u];
    edge[tot].cut=false;
    head[u]=tot++;

}

int DFN[MAXN],LOW[MAXN];
int Index,brige;

int Targan(int u,int pre){
    DFN[u]=LOW[u]=++Index;

    int v;
    for(int i=head[u];i!=-1;i=edge[i].next){
        v=edge[i].to;

        if(v==pre) continue;
        if(!DFN[v]){
            Targan(v,u);
            if(LOW[u]>LOW[v])
                LOW[u]=LOW[v];

            if(LOW[v]>DFN[u]){
                brige++;
                edge[i].cut=true;
                edge[i^1].cut=true;
            }
        }else if(LOW[u]>DFN[v])
            LOW[u]=DFN[v];
    }
}

void solve(int N){
    memset(DFN,0,sizeof(DFN));
    Index=brige=0;
    for(int i=1;i<=N;i++)
        if(!DFN[i])
            Targan(i,i);

    printf("%d critical links
",brige);
    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
",ans[i].first-1,ans[i].second-1);
    printf("
");
}

int main(){
    int n;
    while(scanf("%d",&n)!=EOF){
       init();
      for(int j=0;j<n;j++){

        int u,k,v;
        scanf("%d (%d)",&u,&k);
        u++;
        for(int i=0;i<k;i++){
            scanf("%d",&v);
            v++;
            addEdge(u,v);
            addEdge(v,u);
        }
      }
    solve(n);
    }

}