[kuangbin带你飞]专题九 连通图C - Critical Links UVA - 796

#include<iostream>
#include<string.h>
#include<algorithm>
#include<stdio.h>
using namespace std;
const int SIZE = 100010;
struct node{
  int u,v;
}brige[SIZE];
int head[SIZE],ver[SIZE*2],Next[SIZE*2];
int dfn[SIZE],low[SIZE],n,m,tot,num,cnt;
void add(int x,int y){
   ver[++tot]=y,Next[tot]=head[x],head[x]=tot;
}
void tarjan(int u,int pre){
  dfn[u]=low[u]=++num;
  for (int i=head[u];i;i=Next[i]){
    int v=ver[i];
    if (v==pre)continue;
    if (!dfn[v]){
        tarjan(v,u);
        low[u]=min(low[u],low[v]);
        if (low[v]>dfn[u]){
            /*
            在和u相邻的节点中，存在一个节点是最小的时间戳都比
            当前u的访问次序要大，也就是说这个点是只能通过果u到达，那么
            他们之间相邻的边就是的桥
            */
            cnt++;
            brige[cnt].u=u;
            brige[cnt].v=v;
            if (brige[cnt].u>brige[cnt].v){
                swap(brige[cnt].u,brige[cnt].v);
            }
        }
    }
    else if (low[u]>dfn[v])
        low[u]=min(low[u],dfn[v]);
  }
}
void init(){
   memset(brige,0,sizeof(brige));
   memset(low,0,sizeof(low));
   memset(ver,0,sizeof(ver));
   memset(dfn,0,sizeof(dfn));
   memset(Next,0,sizeof(Next));
   memset(head,0,sizeof(head));
   cnt=0;
   num=0;
   tot=1;
}
bool cmp(node a,node b){
   if (a.u==b.u)return a.v<b.v;
   return a.u<b.u;
}
int main(){
  int id,tmp,nx;
  while(~scanf("%d",&n)){
    if (n==0){
        printf("0 critical links\n\n");
        continue;
    }
    init();
    for(int i=1;i<=n;i++){
        scanf("%d",&id);
        id++;
        getchar();
        getchar();
        scanf("%d",&tmp);
        getchar();
        for (int j=1;j<=tmp;j++){
            scanf("%d",&nx);
            nx++;
            add(id,nx);
            add(nx,id);
        }
    }
    for (int i=1;i<=n;i++){
        if(!dfn[i])tarjan(i,i);
    }
    printf("%d  critical links\n",cnt);
    sort(brige+1,brige+1+cnt,cmp);
    for (int i=1;i<=cnt;i++){
        printf("%d - %d\n",brige[i].u-1,brige[i].v-1);
    }
   printf("\n");

  }
  return 0;
}
/*
3 critical links
0 - 1
3 - 4
6 - 7

*/