UVA - 796（求无向图中的桥）

UVa796

#include<iostream>//tarjan
#include<cstdio>
#include<cstdlib>
#include<string>
#include<vector>
#include<algorithm>
#include<stack>
#include<cstring>
using namespace std;
const int maxn=10005;
vector<int> v[maxn];
int dfn[maxn],low[maxn],par[maxn],cnt;
struct Edge{
    int s,e;
    bool friend operator <(Edge a,Edge b)
    {
        if(a.s==b.s)return a.e<b.e;
        return a.s<b.s;
    }
}bridge[maxn];
int n;
void init()
{
    for(int i=0;i<=n;i++){
        v[i].clear();
    }
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(par,0,sizeof(0));
    cnt=0;
}
void tarjan(int u,int fa)
{
    dfn[u]=low[u]=++cnt;
    par[u]=fa;
    for(int i=0;i<v[u].size();i++){
        int x=v[u][i];
        if(!dfn[x]){
            tarjan(x,u);
            low[u]=min(low[u],low[x]);
        }
        else
        if(fa!=x){
            low[u]=min(low[u],dfn[x]);
        }
    }
}
void slove()
{
    int ans=0;
    for(int i=0;i<n;i++){//图不一定连通，要循环求tarjan
        if(!dfn[i]){
            tarjan(i,-1);
        }
    }
    for(int i=0;i<n;i++){
        int u=par[i];
        int v=i;
        if(u!=-1){
            if(low[v]>dfn[u]){
                bridge[ans].s=u;
                bridge[ans].e=v;
                if(bridge[ans].s>bridge[ans].e){
                    swap(bridge[ans].s,bridge[ans].e);
                }
                ans++;
            }
        }
    }
    sort(bridge,bridge+ans);
    printf("%d critical links\n",ans);
    for(int i=0;i<ans;i++){
        printf("%d - %d\n",bridge[i].s,bridge[i].e);
    }
    printf("\n");
}
int main()
{
    while(scanf("%d",&n)!=EOF){
        init();
        for(int i=0;i<n;i++){
        int s,m;
        scanf("%d (%d)",&s,&m);
        while(m--){
           int e;
           scanf("%d",&e);
           v[s].push_back(e);
           v[e].push_back(s);
          // printf("%d %d\n",s,e);
        }
        }
       /* for(int i=0;i<n;i++){
            for(int j=0;j<v[i].size();j++){
                printf("%d %d\n",i,v[i][j]);
            }
            printf("\n");
        }*/
        slove();
    }
    return 0;
}