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
",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
",ans[i].first - 1,ans[i].second -1);
}
printf("
");
}
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;
}