无向图求割边

//无向图求割边
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
#include <stack>
#include <vector>
#include <deque>
#include <map>
#include <iostream>
using namespace std;
typedef long long LL;
const double pi = acos(-1.0);
const double e = exp(1);
//const int MAXN =2e5+10;
const LL N = 1000000007;

struct edge{
    int w;
    int to;
    int next;    
}edge[200009];
int head[200009];

int dfn[100009];
int low[100009];
int cnt = 1;

void tarjan(int u, int fa)
{
    
    int i;
    low[u] = dfn[u] = cnt++;
    for(i = head[u]; i != -1; i = edge[i].next)
    {
        //cout << u << " " << fa << endl;
        int v = edge[i].to;
        if(!dfn[v])
        {
            //cout << "** " <<  v << " " << u << endl;
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if(low[v] > dfn[u])
            {
                printf("%d ---> %d
", u, v);
            } 
        }
        else if(v != fa)
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
}

int main()
{
    int n,m, i;
    int cnt1, a, b;
    while(scanf("%d%d", &n,&m) != EOF)
    {
        if(n == 0 && m == 0)
            break;
        cnt1 = 0;
        cnt = 1;
        memset(head, -1, sizeof(head));
        memset(dfn, 0, sizeof(dfn));
        memset(low, 0, sizeof(low));
        while(m--)
        {
            scanf("%d%d", &a,&b);
            
            edge[cnt1].to = b;
            edge[cnt1].next = head[a];
            head[a] = cnt1++;

            edge[cnt1].to = a;
            edge[cnt1].next = head[b];
            head[b] = cnt1++;
        }
        for(i = 1; i <= n; i++)
        {
            if(!dfn[i])
            {
                tarjan(i, 0);
            }
        }
        
    }
    return 0;
}