Network POJ - 3694 （连通图标求桥）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>
#include <stack>
#include <algorithm>
#include <cmath>
#define mem(a, b) memset(a, b, sizeof(a))
using namespace std;
const int maxn = 10010, INF = 0x7fffffff;
int pre[maxn], low[maxn], iscut[maxn];
int dfs_clock, n, cnt;
vector<int> G[maxn];
struct edge
{
    int u, v;
}Edge[maxn];
int cmp(edge a, edge b)
{
    if(a.u == b.u) return a.v < b.v;
    return a.u < b.u;
}

int dfs(int u, int fa)
{
    int lowu = pre[u] = ++dfs_clock;
    int child = 0;
    for(int i=0; i<G[u].size(); i++)
    {
        int v = G[u][i];
        if(!pre[v])
        {
            child++;
            int lowv = dfs(v, u);
            lowu = min(lowu, lowv);
            if(lowv > pre[u])
            {
                iscut[u] = 1;
                Edge[cnt].u = u, Edge[cnt].v = v;
                if(Edge[cnt].u > Edge[cnt].v) swap(Edge[cnt].u, Edge[cnt].v);
                cnt++;
            }

        }
        else if(pre[v] < pre[u] && v != fa)
            lowu = min(lowu, pre[v]);
    }
    if(fa < 0 && child == 1) iscut[u] = 0;
    low[u] = lowu;
    return lowu;
}

void init()
{
    cnt = 0;
    dfs_clock = 0;
    mem(pre, 0);
    mem(low, 0);
    mem(iscut, 0);
    for(int i=0; i<=n; i++) G[i].clear();
}

int main()
{
    while(cin>> n)
    {
        init();
        for(int i=0; i<n; i++)
        {
            int u, d, v;
            scanf("%d (%d)", &u, &d);
            for(int i=0; i<d; i++)
            {
                cin>> v;
                G[u].push_back(v);
                G[v].push_back(u);
            }
        }
        for(int i=0; i<n; i++)
            if(!pre[i])
                dfs(i, -1);
        sort(Edge, Edge+cnt, cmp);
        printf("%d critical links\n",cnt);
        for(int i=0; i<cnt; i++)
            cout<< Edge[i].u << " - " << Edge[i].v <<endl;
        cout<<endl;
    }
    return 0;
}