http://poj.org/problem?id=3352
https://blog.csdn.net/zstuyyyyccccbbbb/article/details/108904709(原题链接)
#include<iostream>
#include<vector>
#include<queue>
#include<stack>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=1e3+100;
typedef long long LL;
LL dfn[maxn],low[maxn],fa[maxn],times=0,cnt=0,col[maxn],du[maxn];
vector<LL>g[maxn];
stack<LL>s;
bool ma[maxn][maxn],instack[maxn];
void tarjan2(LL x){dfn[x]=low[x]=++times;s.push(x);instack[x]=true;for(LL i=0;i<g[x].size();i++){LL to=g[x][i];if(!dfn[to]){fa[to]=x;tarjan2(to);low[x]=min(low[x],low[to]);}else if(to!=fa[x]) low[x]=min(low[x],dfn[to]);}if(low[x]==dfn[x]){cnt++;LL y;do{y=s.top();col[y]=cnt;instack[y]=false;s.pop();}while(y!=x);return;}
}
int main(void)
{cin.tie(0);std::ios::sync_with_stdio(false);LL n,m;cin>>n>>m;memset(fa,-1,sizeof(fa));for(LL i=1;i<=m;i++){LL u,v;cin>>u>>v;if(!ma[u][v]) g[u].push_back(v),g[v].push_back(u);ma[u][v]++,ma[v][u]++;}for(LL i=1;i<=n;i++) if(!dfn[i]) tarjan2(i);for(LL i=1;i<=n;i++){for(LL j=0;j<g[i].size();j++){if(col[i]!=col[g[i][j]]) du[col[i]]++,du[col[g[i][j]]]++;}}LL sum=0;for(LL i=1;i<=cnt;i++){if(du[i]/2==1) sum++;}cout<<(sum+1)/2<<endl;
return 0;
}