一道简单的双联通求桥的题目，，数据时字符串，，map用的不熟练啊，，，，，，，，，，，，，
#include <iostream>
#include <cstring>
#include <cstdio>
#include <map>
#include <string>
#include <algorithm>
#define N 10001
using namespace std;
int head[N],num,dfs[N],low[N],n,m,idx,bridge[N],bum;
struct edge
{
int st,ed,next;
}E[N*20];
void addedge(int x,int y)
{
E[num].st=x;
E[num].ed=y;
E[num].next=head[x];
head[x]=num++;
}
int cmp(const void *a,const void *b)
{
return *(int *)a-*(int *)b;
}
void Tarjan(int u,int father)
{
int i,v;
low[u]=dfs[u]=idx++;
for(i=head[u];i!=-1;i=E[i].next)
{
v=E[i].ed;
if(v==father)continue;
if(dfs[v]==-1)
{
Tarjan(v,u);
low[u]=low[u]>low[v]?low[v]:low[u];
if(low[v]>dfs[u])//桥
{
bridge[bum++]=i;
}
}
else low[u]=low[u]>dfs[v]?dfs[v]:low[u];
}
}
int main()
{
int i,x,y,j,t,sum;
char str[2][200];
scanf("%d",&t);
while(t--)
{
scanf("%d%d",&n,&m);
memset(head,-1,sizeof(head));
num=0;sum=1;
map<string,int>mp;
map<int,string>mmp;
for(i=0;i<m;i++)
{
scanf("%s%s",str[0],str[1]);
if(mp[str[0]]==0)
{
mp[str[0]]=sum;
mmp[sum]=str[0];
sum++;
}
if(mp[str[1]]==0)
{
mp[str[1]]=sum;
mmp[sum]=str[1];
sum++;
}
x=mp[str[0]];
y=mp[str[1]];
addedge(x,y);
addedge(y,x);
}
memset(dfs,-1,sizeof(dfs));
idx=0;
bum=0;
Tarjan(1,-1);
for(i=1;i<=n;i++)
{
if(dfs[i]==-1)
break;
}
if(i<=n){printf("0
");continue;}
printf("%d
",bum);
qsort(bridge,bum,sizeof(bridge[0]),cmp);
for(j=0;j<bum;j++)
{
i=bridge[j];
i=(i/2*2);
x=E[i].st;
y=E[i].ed;
if(x!=y)
printf("%s %s
",mmp[E[i].st].c_str(),mmp[E[i].ed].c_str());
}
}
return 0;
}