poj3177 && poj3352 边双连通分量缩点

/*
 * Author:  sweat123
 * Created Time:  2016/6/21 20:07:00
 * File Name: main.cpp
 */
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<cmath>
#include<string>
#include<vector>
#include<cstdio>
#include<time.h>
#include<cstring>
#include<iostream>
#include<algorithm>
#define INF 1<<30
#define MOD 1000000007
#define ll long long
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define pi acos(-1.0)
using namespace std;
const int MAXN = 5010;
struct node{
    int to;
    int next;  
}edge[MAXN<<2];
int pre[MAXN],vis[MAXN],pa[MAXN],dfn[MAXN],low[MAXN],n,m,ind;
int px[MAXN],py[MAXN];
int pcnt;
void add(int x,int y){
    edge[ind].to = y;
    edge[ind].next = pre[x];
    pre[x] = ind ++;   
}
int find(int x){
    if(pa[x] != x)pa[x] = find(pa[x]);
    return pa[x];   
}
void dfs(int rt,int k,int fa){
    dfn[rt] = low[rt] = k;
    for(int i = pre[rt]; i != -1; i = edge[i].next){
        int t = edge[i].to;
        if(!dfn[t] && t != fa){
            dfs(t,k+1,rt);
            low[rt] = min(low[rt],low[t]);
            if(low[t] > dfn[rt]){
                px[pcnt] = rt,py[pcnt++] = t;
            } else {
                int fx = find(t);
                int fy = find(rt);
                if(pa[fx] != pa[fy]){
                    pa[fx] = fy;   
                }
            } 
        } else if(t != fa){//bridge is differenet from point
            low[rt] = min(low[rt],dfn[t]);  
        }
    }   
}
int d[MAXN],f[MAXN];
int main(){
    while(~scanf("%d%d",&n,&m)){
        ind = 0;
        pcnt = 0;
        memset(pre,-1,sizeof(pre));
        for(int i = 1; i <= m; i++){
            int x,y;
            scanf("%d%d",&x,&y);
            add(x,y),add(y,x);
        }  
        for(int i = 1; i <= n; i++){
            pa[i] = i;   
        }
        memset(dfn,0,sizeof(dfn));
        memset(low,0,sizeof(low));
        dfs(1,1,-1);
        //for(int i = 1; i <= n; i++){
            //cout<<dfn[i]<<‘ ‘<<low[i]<<endl;
        //}
        //cout<<endl; 
        memset(d,0,sizeof(d));
        memset(f,-1,sizeof(f));
        int pnum = 0;
        for(int i = 1; i <= n; i++){
            int fx = find(i);
            if(f[fx] == -1)f[fx] = ++pnum;
            f[i] = f[fx];
        }
        for(int i = 0; i < pcnt; i++){
            d[f[px[i]]] ++,d[f[py[i]]] ++;   
        }
        int ans = 0;
        for(int i = 1; i <= pnum; i++){
            if(d[i] == 1)ans ++;   
        }
        printf("%d\n",(ans + 1) / 2);
    }
    return 0;
}