【HDOJ】4587 TWO NODES

Tarjan解无向图的割点和桥，参考白书。

 1 /* 4587 */
 2 #include <iostream>
 3 #include <vector>
 4 #include <algorithm>
 5 #include <cstdio>
 6 #include <cstring>
 7 #include <cstdlib>
 8 using namespace std;
 9
10 #define MAXN 5005
11
12 vector<int> vc[MAXN];
13 int dfs_clock;
14 int cnt[MAXN];
15 int pre[MAXN];
16 int n, m, cur;
17
18 int Tarjan(int u, int fa) {
19     int i, j, k, v;
20     int lowu, lowv;
21     int child = 0;
22
23     lowu = pre[u] = ++dfs_clock;
24     for (i=0; i<vc[u].size(); ++i) {
25         v = vc[u][i];
26         if (v==fa || v==cur)
27             continue;
28         if (!pre[v]) {
29             ++child;
30             lowv = Tarjan(v, u);
31             lowu = min(lowu, lowv);
32             if (lowv >= pre[u])
33                 ++cnt[u];
34         } else if (pre[v] < pre[u])
35             lowu = min(lowu, pre[v]);
36     }
37     if (fa < 0)
38         cnt[u] = child - 1;
39     return lowu;
40 }
41
42 void init() {
43     dfs_clock = 0;
44     memset(cnt, 0, sizeof(int)*n);
45     memset(pre, 0, sizeof(int)*n);
46 }
47
48 int main() {
49     int i, j, k;
50     int ans;
51
52     #ifndef ONLINE_JUDGE
53         freopen("data.in", "r", stdin);
54     #endif
55
56     while (scanf("%d %d", &n, &m)!=EOF) {
57         for (i=0; i<n; ++i)
58             vc[i].clear();
59         while (m--) {
60             scanf("%d %d", &i, &j);
61             vc[i].push_back(j);
62             vc[j].push_back(i);
63         }
64         ans = 0;
65         for (cur=0; cur<n; ++cur) {
66             init();
67             k = 0;
68             for (i=0; i<n; ++i) {
69                 if (i!=cur && !pre[i]) {
70                     ++k;
71                     Tarjan(i, -1);
72                 }
73             }
74             for (i=0; i<n; ++i)
75                 if (i!=cur)
76                     ans = max(ans, k+cnt[i]);
77         }
78         printf("%d\n", ans);
79     }
80
81     return 0;
82 }