poj-3177（并查集+双联通分量+Tarjan算法）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
const int maxn = 10010;
struct Edge{
    int u,v;
};
Edge tmp;
vector <Edge> ee;
int num[maxn],vis[maxn],low[maxn],fa[maxn],tog[maxn],m,n,tim;
vector <int> vc[maxn];
void Init()
{
    memset(vis,0,sizeof(vis));
    memset(num,0,sizeof(num));
    memset(low,0,sizeof(low));
    memset(fa,0,sizeof(fa));
    memset(tog,0,sizeof(tog));
    ee.clear();
    for(int i=0;i<maxn;i++) vc[i].clear();
    tim=1;
}
int MIN(int x,int y)
{
    return x<y?x:y;
}
int f(int x)
{
    if(fa[x]==0) return x;
    else return fa[x]=f(fa[x]);
}
void Tarjan(int v,int pre)
{
    int i,w;
    vis[v]=1;
    low[v]=num[v]=tim++;
    for(i=0;i<vc[v].size();i++){
        w=vc[v][i];
        if(!vis[w]){
            Tarjan(w,v);
            low[v]=MIN(low[v],low[w]);
            if(low[w]>num[v]){
                tmp.u=v;tmp.v=w;
                ee.push_back(tmp);
            }
            else{
                int t1=f(v);
                int t2=f(w);
                if(t1!=t2) fa[t2]=t1;
            }
        }
        else if(pre!=w) low[v]=MIN(low[v],num[w]);
    }
}
int main(void)
{
    int i,j,x,y;
    while(~scanf("%d%d",&n,&m)){
        Init();
        for(i=0;i<m;i++){
            scanf("%d%d",&x,&y);
            vc[x].push_back(y);
            vc[y].push_back(x);
        }
        Tarjan(1,-1);
        for(i=0;i<ee.size();i++){
            int t1=f(ee[i].u);
            int t2=f(ee[i].v);
            tog[t1]++;tog[t2]++;
        }
        int cnt=0;
        for(i=1;i<=n;i++)
        if(tog[i]==1) cnt++;
        cnt=(cnt+1)/2;
        printf("%d\n",cnt);
    }
    return 0;
}