UVA 796 求割边

#include <bits/stdc++.h>

using namespace std;
#define ll long long
#define mem(a, b) memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
#define DBG printf("this is a input\n")
#define fi first
#define se second
#define mk(a, b) make_pair(a,b)
#define p_queue priority_queue

ll gcd(ll a, ll b) {
    return b == 0 ? a : gcd(b, a % b);
}

ll lcm(ll a, ll b) {
    return a / gcd(a, b) * b;
}
const int MAXN = 10005;
int n, cnt, brige, head[MAXN];
int low[MAXN] , dfn[MAXN], times;
struct e
{
    int f, t , next;
    int cut;
}edge[MAXN*10];
void add(int f, int t)
{
    edge[cnt].t = t;
    edge[cnt].cut = 0;
    edge[cnt].f = f;
    edge[cnt].next = head[f];
    head[f] = cnt ++;
}
void Init()
{
    cnt = 0, brige = 0, times = 0;
    mem(head,-1);
    mem(low,0);
    mem(dfn,0);
}
void tarjan(int u , int pre)
{
    dfn[u] = low[u] = ++times;
    for (int i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].t;
        if(v == pre) continue;
        if(!dfn[v])
        {
            tarjan(v,u);
            low[u] = min(low[u],low[v]);
            if(low[v] > dfn[u])
            {
                brige ++;
                edge[i].cut = 1;
                edge[i^1].cut = 1;
            }
        }
        else
            low[u] = min(low[u],dfn[v]);
    }
}
void solve()
{
    for(int i = 1 ; i <= n ; i ++)
    {
        if(!dfn[i])
            tarjan(i,i);
    }
    printf("%d critical links\n",brige);
    vector<pair<int,int> > ve;
    for(int i = 0 ; i < cnt ; i ++)
    {
        if(edge[i].cut && edge[i].t > edge[i].f)
            ve.push_back(mk(edge[i].f,edge[i].t));
    }
    sort(ve.begin(), ve.end());
    for(int i = 0;i < ve.size();i++)
        printf("%d - %d\n",ve[i].first-1,ve[i].second-1);
    printf("\n");
}
int main(void)
{
    while(scanf("%d",&n) != EOF)
    {
        int u , v, k;
        Init();
        for(int i = 1 ; i <= n ; i ++)
        {
            scanf("%d (%d)",&u,&k);
            u ++;
            while(k --)
            {
                scanf("%d",&v);
                v ++;
                if(v <= u) //当作有向边处理，避免重边
                    continue;
                add(u,v);
                add(v,u);
            }
        }
        solve();
    }
}