Redundant Paths POJ - 3177（边—双连通分量）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
#include <stack>
#define mem(a, b) memset(a, b, sizeof(a))
using namespace std;
const int maxn = 5005, INF = 0x7fffffff;
int dfn[maxn], low[maxn], drgee[maxn];
bool graph[5005][5005];
int dfs_clock, n, m, ret;
vector<int> G[maxn];
void init()
{
    for(int i=0; i<=n; i++) G[i].clear();
    ret = 0;
    dfs_clock = 0;
    mem(low, 0);
    mem(dfn, 0);
    mem(drgee, 0);
    mem(graph, 0);
}

void tarjan(int u, int fa)
{
    dfn[u] = low[u] = ++dfs_clock;
    for(int i=0; i<G[u].size(); i++)
    {
        int v = G[u][i];
        if(!dfn[v])
        {
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
        }
        else if(v != fa)
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
}

int main()
{

   while(cin>> n >> m){
    init();
    for(int i=0; i<m; i++)
    {
        int u, v;
        cin>> u >> v;
        if(!graph[u][v])
        {
            graph[u][v] = graph[v][u] = 1;
            G[u].push_back(v);
            G[v].push_back(u);
        }
    }
    tarjan(1, -1);
    for(int i=1; i<=n; i++)
        for(int j=0; j<G[i].size(); j++)
            if(low[i] != low[G[i][j]])
                drgee[low[i]]++;
    for(int i=0; i<=n; i++)
        if(drgee[i] == 1)
            ret++;
    cout<< (ret+1)/2 <<endl;
   }


    return 0;
}