Poj 1655 Balancing Act (树的重心)

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 #include <algorithm>
 5 using namespace std;
 6 const int maxn = 20010;
 7 const int INF = 0x3f3f3f3f;
 8 struct node
 9 {
10     int to, next;
11 } edge[maxn * 2];
12 int head[maxn], vis[maxn], son[maxn];
13 int tot, ans, num, n;
14 void init ()
15 {
16     tot = 0;
17     num = INF;
18     memset (head, -1, sizeof(head));
19     memset (vis, 0, sizeof(vis));
20     memset (son, 0, sizeof(son));
21 }
22 void Add (int from, int to)
23 {
24     edge[tot].to = to;
25     edge[tot].next = head[from];
26     head[from] = tot ++;
27 }
28 void dfs (int u)
29 {
30     vis[u] = 1;
31     int nu = 0;
32     for (int i=head[u]; i!=-1; i=edge[i].next)
33     {
34         int v = edge[i].to;
35         if (!vis[v])
36         {
37             dfs (v);
38             son[u] += son[v] + 1;//u的子节点数目
39             nu = max (nu , son[v] + 1);//u的子树最大的节点数目
40         }
41 
42     }
43     nu = max (nu, n-son[u]-1);//(u子树最大节点数目,u点向上的节点数目)
44     if (nu<num || num==nu && ans>u)
45     {
46         num = nu;
47         ans = u;
48     }
49 }
50 int main ()
51 {
52     int t;
53     scanf ("%d", &t);
54     while (t --)
55     {
56         init ();
57         scanf ("%d", &n);
58         for (int i=1; i<n; i++)
59         {
60             int u, v;
61             scanf ("%d %d", &u, &v);
62             Add (u, v);
63             Add (v, u);
64         }
65         dfs (1);
66         printf ("%d %d\n", ans, num);
67     }
68     return 0;
69 }