2014 UESTC Training for Graph Theory B

#include <map>
#include <set>
#include <list>
#include <cmath>
#include<cctype>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b)
{
return a % b == 0 ? b : gcd(b, a % b);
}
#define MAXN 100002
int degree[MAXN];
int pre[MAXN],lowlink[MAXN];
int dfs_clock,scc_cnt;
vector <int>G[MAXN];
int N,M;
void dfs(int u,int fa)
{
pre[u]=lowlink[u]=++dfs_clock;
for (int i=0;i<(int)G[u].size();i++)
{
int v=G[u][i];
if (!pre[v])
{
dfs(v,u);
lowlink[u]=min(lowlink[u],lowlink[v]);
}
if (v!=fa)
{
lowlink[u]=min(lowlink[u],pre[v]);
}
}
}
void init()
{
dfs_clock=scc_cnt=0;
memset(pre,0,sizeof(pre));
memset(lowlink,0,sizeof(lowlink));
int a,b;
memset(degree,0,sizeof(degree));
for (int i=0;i<=N;i++) G[i].clear();
for (int i=0;i<M;i++)
{
scanf("%d%d",&a,&b);
G[a].push_back(b);
G[b].push_back(a);
}

}
int main()
{
//freopen("sample.txt","r",stdin);
while (scanf("%d%d",&N,&M)!=EOF)
{
init();
dfs(1,-1);
for (int u=1;u<=N;u++)
for (int i=0;i<(int)G[u].size();i++)
{
int v=G[u][i];
if (lowlink[u]!=lowlink[v]) degree[lowlink[v]]++;
}
//for (int i=0;i<N;i++) printf("%d\n",lowlink[i]);
int ans=0;
for (int i=1;i<=N;i++)
if (degree[i]==1) ans++;
printf("%d\n",(ans+1)/2);
}
return 0;
}