12388. 图论割边

 1 #include <cstdio>
 2 #include <vector>
 3 #include <cstring>
 4 
 5 
 6 using namespace std;
 7 
 8 
 9 const int max_n = 1e5 + 10;
10 int n,m;
11 int num[max_n],low[max_n];
12 int time_index,a,b;
13 vector<int> g[max_n];
14 int ans;
15 
16 
17 void dfs(int cur,int fa)
18 {
19     ++time_index;
20     num[cur]=time_index;
21     low[cur]=time_index;
22 
23     for(int i=0;i<g[cur].size();++i)
24     {
25         int v=g[cur][i];
26         if(num[v]==0)
27         {
28             dfs(v,cur);
29             low[cur]=min(low[cur],low[v]);
30             if(low[v]>num[cur])
31             {
32                 ++ans;
33             }
34         }
35         else if(fa!=v)
36         {
37             low[cur]=min(low[cur],num[v]);
38         }
39     }
40 }
41 
42 void solve()
43 {
44     ans=0;
45     time_index=0;
46     memset(num,0,sizeof(num));
47 
48     dfs(1,1);
49 
50     printf("%d",ans);
51 }
52 
53 
54 int main()
55 {
56     scanf("%d %d",&n,&m);
57     for(int i=0;i<m;++i)
58     {
59         scanf("%d %d",&a,&b);
60         g[a].push_back(b);
61         g[b].push_back(a);
62     }
63 
64     solve();
65 
66     return 0;
67 }