poj 1144 割点

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 using namespace std;
 5 
 6 const int N = 200;
 7 const int M = 500;
 8 int dfn[N];
 9 int low[N];
10 int head[N];
11 bool is_cut[N];
12 int n, e, dfs_clock;
13 
14 void init()
15 {
16     e = dfs_clock = 0;
17     memset( head, -1, sizeof(head) );
18     memset( dfn, 0, sizeof(dfn) );
19     memset( is_cut, 0, sizeof(is_cut) );
20 }
21 
22 struct Edge 
23 {
24     int v, next;
25 } edge[M];
26 
27 void addEdge( int u, int v )
28 {
29     edge[e].v = v;
30     edge[e].next = head[u];
31     head[u] = e++;
32 }
33 
34 void dfs( int u, int fa )
35 {
36     low[u] = dfn[u] = ++dfs_clock;
37     int cnt = 0;
38     for ( int i = head[u]; i != -1; i = edge[i].next )
39     {
40         int v = edge[i].v;
41         if ( !dfn[v] )
42         {
43             cnt++;
44             dfs( v, u );
45             if ( low[v] >= dfn[u] ) is_cut[u] = true;
46             low[u] = min( low[u], low[v] );
47         }
48         else if ( v != fa )
49         {
50             low[u] = min( low[u], dfn[v] );
51         }
52     }
53     if ( fa < 0 && cnt == 1 ) is_cut[u] = false;
54 }
55 
56 int main ()
57 {
58     while ( scanf("%d", &n), n )
59     {
60         init();
61         int u, v;
62         while ( scanf("%d", &u), u )
63         {
64             while ( getchar() != ‘\n‘ )
65             {
66                 scanf("%d", &v);
67                 addEdge( u, v );
68                 addEdge( v, u );
69             }
70         }
71         dfs( 1, -1 );
72         int ans = 0;
73         for ( int i = 1; i <= n; i++ )
74         {
75             if ( is_cut[i] ) ans++;
76         }
77         printf("%d\n", ans);
78     }
79     return 0;
80 }