uva796 Critical Links（求桥并按边输出）

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <limits>
#include <queue>
#include <stack>
#include <vector>
#include <map>

using namespace std;

#define N 12005
#define INF 0xfffffff
#define PI acos (-1.0)
#define EPS 1e-8

struct node
{
int x, y;
bool friend operator < (node a, node b)
{
if (a.x == a.y) return a.y < b.y;
return a.x < b.x;
}
}bridge
;

vector <int> G
;
int n, low
, dfn
, f
, Time, ans;

void Init ();
void solve ();
void tarjan (int u, int fa);

int main ()
{
while (~scanf ("%d", &n))
{
Init ();
for (int i=0; i<n; i++)
{
int a, b, m;
scanf ("%d (%d)", &a, &m);
while (m--)
{
scanf ("%d", &b);
G[a].push_back (b);
G[b].push_back (a);
}
}
solve ();
}
return 0;
}

void Init ()
{
memset (low, 0, sizeof (low));
memset (dfn, 0, sizeof (dfn));
memset (f, 0, sizeof (f));
Time = 0;
for (int i=0; i<n; i++)
G[i].clear ();
}

void solve ()
{
ans = 0;
for (int i=0; i<n; i++)
if (!low[i])
tarjan (i, -1);

for (int i=0; i<n; i++)
{
int v = f[i];
if (v != -1 && dfn[v] < low[i])
{
bridge[ans].x = i;
bridge[ans].y = v;
if (bridge[ans].x > bridge[ans].y)
swap (bridge[ans].x, bridge[ans].y);
ans++;
}
}

sort (bridge, bridge+ans);

printf ("%d critical links\n", ans);
for (int i=0; i<ans; i++)
printf ("%d - %d\n", bridge[i].x, bridge[i].y);
puts ("");
}

void tarjan (int u, int fa)
{
low[u] = dfn[u] = ++Time;
f[u] = fa;
int len = G[u].size (), v;

for (int i=0; i<len; i++)
{
v = G[u][i];
if (!low[v])
{
tarjan (v, u);
low[u] = min (low[u], low[v]);
}
else if (fa != v)
low[u] = min (low[u], dfn[v]);
}
}