C++ :

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
struct Edge{
    int u,
        v;
}edge[1003];
vector<int> Vec[1003];
int vis[1003];
int from, to;
bool Go = false;
void dfs(int n, int u)
{
    vis[n] = 1;
    if(n == to)Go = true;
    if(Go == true)return;
    for(int i=0; i<Vec[n].size(); i++){
        if((vis[Vec[n][i]] == 0) && (Vec[n][i] == to || Vec[n][i] != u)){//下一个点没被访问过和下一个点。。
            dfs(Vec[n][i], u);
            vis[Vec[n][i]] = 0;
        }
    }
}
int main()
{
    int i, j, n, m, u, v;
    int count;
    cin>> n >> m;
    for(i=1; i<=m; i++){
        cin>> u >> v;
        Vec[u].push_back(v);
        Vec[v].push_back(u);
    }
    cin>> from >> to;
    count = 0;
    dfs(from, -1);
    if(Go == false){
        cout<<"-1\n";
    }
    else
        for(i=1; i<=m; i++){
            Go = false;
            memset(vis, 0, sizeof(vis));
            dfs(from, i);
            if(Go == false)count++;
        }
    cout<<count<<endl;
    return 0;
}

Java :

import java.util.ArrayList;
import java.util.Scanner;

public class Main {
	public static ArrayList ff;
	public static int flag;
	public static int[] f;
	public static ArrayList c;
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		while(sc.hasNext()) {
			int n=sc.nextInt();
			int m=sc.nextInt();
			ArrayList<Integer>[] a=new ArrayList[n+1];
			for(int i=0;i<n+1;i++) {
				a[i]=new ArrayList();
			}
            f=new int[n+1];
			ff=new ArrayList();
			for(int i=0;i<m;i++) {
				int x=sc.nextInt();
				int y=sc.nextInt();
				a[x].add(y);
				a[y].add(x);

			}
			c=new ArrayList();
			int s=0;
			int begin=sc.nextInt();
			int end =sc.nextInt();
			c.add(begin);
			f[begin]=1;
			fds(a,begin,end,-1);

			if(flag!=0) {
				c.clear();
				for(int k=1;k<f.length;k++) {
					f[k]=0;
				}
				for(int i=0;i<ff.size();i++) {
					flag=0;
					fds(a,begin,end,(int) ff.get(i));
					if(flag==0) {
						s++;
						}
				}
			}else {
				s=-1;
			}
			flag=0;
			ff.clear();
			c.clear();
			for(int k=1;k<f.length;k++) {
				f[k]=0;
			}
			System.out.println(s);
			
		}
	}
	public static void fds (ArrayList[] a,int d,int end,int p) {
		for(int i=0;i<a[d].size();i++) {
			if(f[(int)a[d].get(i)]==0&&(int)a[d].get(i)!=p) {
				if((int)a[d].get(i)==end) {
					if(p==-1) {

					for(int k=1;k<c.size();k++) {
						ff.add(c.get(k));
					}
					}
					flag=2;
					return;
				}
			

				f[(int)a[d].get(i)]=1;
				int e=(int)a[d].get(i);
				c.add(a[d].get(i));
				fds(a,e,end,p);
				f[(int)a[d].get(i)]=0;
				if(flag==2) {
					break;
					}c.remove(c.size()-1);
			
				
			}
		}
	}
}