lightoj 1063 求割点

题目链接：http://lightoj.com/volume_showproblem.php?problem=1063

#include<cstdio>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
const int maxn = 10050;
const int INF = 0x3f3f3f;

vector<int> G[maxn];
int pre[maxn],low[maxn],dfs_clock;
bool iscut[maxn];
int ans;
int n,m;

void tarjan(int u,int fa){
    pre[u] = low[u] = dfs_clock++;
    int child = 0;
    for(int i=0;i<G[u].size();i++){
        int v = G[u][i];
        if(v == fa)  continue;
        if(!pre[v]){
            child++;
            tarjan(v,u);
            low[u] = min(low[u],low[v]);
            if(low[v] >= pre[u])  iscut[u] = true;
        }
        else
            low[u] = min(low[u],pre[v]);
    }
    if(fa == -1 && child == 1)  iscut[u] = false;
}
int main()
{
     //freopen("E:\\acm\\input.txt","r",stdin);
    int T;
    cin>>T;
    for(int t=1;t<=T;t++){
        cin>>n>>m;
        memset(pre,0,sizeof(pre));
        memset(iscut,0,sizeof(iscut));
        dfs_clock = 1;
        ans = 0;
        for(int i=1;i<=n;i++)   G[i].clear();
        for(int i=1;i<=m;i++){
            int a,b;
            scanf("%d %d",&a,&b);
            G[a].push_back(b);
            G[b].push_back(a);
        }
        tarjan(1,-1);
        for(int i=1;i<=n;i++)
            if(iscut[i]) ans++;
        printf("Case %d: %d\n",t,ans);
    }
}