poj 3177 Redundant Paths

#include<map>
#include<set>
#include<stack>
#include<queue>
#include<cmath>
#include<vector>
#include<cstdio>
#include<string>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#define  inf 0x0f0f0f0f
using namespace std;

int degree[5000+10];

struct CUT_E
{
    static const int maxn=5000+10;
    int low[maxn],pre[maxn],dfs_clock,n,m,sumcut;
    int cut_edge[maxn][maxn];
    vector<int>group[maxn];

    void init()
    {
        for (int i=0;i<=n;i++)
        {
            group[i].clear();
            for (int j=0;j<=n;j++)
            cut_edge[i][j]=0;
        }
        sumcut=0; dfs_clock=0;
    }

    void addedge(int u,int v)
    {
        group[u].push_back(v);
        group[v].push_back(u);
    }

    int dfs(int u,int fa)
    {
        int lowu=pre[u]=++dfs_clock;
        for (int i=0;i<group[u].size();i++)
        {
            int v=group[u][i];
            if (!pre[v])
            {
                int lowv=dfs(v,u);
                lowu=min(lowu,lowv);
                if (lowv>pre[u]) {cut_edge[u][v]=1;cut_edge[v][u]=1;}
            }
            else if (pre[v]<pre[u] && v!=fa) lowu=min(lowu,pre[v]);
        }
        low[u]=lowu;
        return lowu;
    }

    int get_sum()
    {
        int ans=dfs(-1,1);
        for (int i=1;i<=n;i++)
        for (int j=1;j<=n;j++)
        if (cut_edge[i][j]) sumcut++;
        return sumcut;
    }
};
CUT_E stable;

void update()
{
    for (int i=0;i<=stable.n;i++) stable.group[i].clear();
    for (int i=1;i<=stable.n;i++)
    for (int j=1;j<=stable.n;j++)
    if (stable.cut_edge[i][j]==2) {
        stable.group[i].push_back(j);
        stable.group[j].push_back(i);
    }
}

bool vis[5000+10];
int p[5000+10];
void DFS(int u,int fa)
{
    p[u]=fa;
    for (int i=0;i<stable.group[u].size();i++)
    {
        int v=stable.group[u][i];
        if(!vis[v])
        {
            vis[v]=true;
            DFS(v,fa);
        }
    }
}


void solve()
{
    for (int i=1;i<=stable.n;i++)
    for (int j=1;j<=stable.n;j++)
    if (stable.cut_edge[i][j]==1)
    {
        int x=p[i];
        int y=p[j];
        degree[x]++;
        degree[y]++;
    }
}

int find_leaf()
{
    int ans=0;
    for (int i=1;i<=stable.n;i++)
    if (degree[i]==2) ans++;
    return ans;
}

int main()
{
    //freopen("in.txt","r",stdin);
    int f,r,x,y;
    while (scanf("%d%d",&f,&r)!=EOF)
    {
        stable.n=f; stable.m=r;
        stable.init();
        for (int i=1;i<=r;i++)
        {
            scanf("%d%d",&x,&y);
            stable.addedge(x,y);
            stable.cut_edge[x][y]=2;
            stable.cut_edge[y][x]=2;
        }
        int temp=stable.dfs(1,-1);//求割边
        update();//去掉割边，更新图
        memset(vis,0,sizeof(vis));vis[1]=true;
        for (int i=1;i<=f;i++)//找出每一个连通快，缩点
        if (!vis[i] || i==1)DFS(i,i);
        memset(degree,0,sizeof(degree));
        solve();
        int leaf=find_leaf();//找度为一的节点
        printf("%d\n",(leaf+1)/2);
    }
    return 0;
}