POJ 3107 Godfather （树形dp）

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <cmath>
 6 #include <algorithm>
 7 #include <vector>
 8 #define LL __int64
 9 const int maxn = 50000+10;
10 const int INF = 1<<28;
11 using namespace std;
12 int head[maxn], vis[maxn], t, d[maxn];
13 int mi, n;
14 struct node
15 {
16     int u, v, ne;
17 }e[2*maxn];
18 
19 void add(int u, int v)
20 {
21     e[t].u = u;
22     e[t].v = v;
23     e[t].ne = head[u];
24     head[u] = t++;
25 }
26 int dfs(int son, int fa)
27 {
28     int i, tmp, sum = 1, x;  //sum是以son为根节点的子树的全部的节点数
29     for(i = head[son]; i != -1; i = e[i].ne)
30     {
31         tmp = e[i].v;
32         if(tmp == fa) continue;  //避免回去。
33         x = dfs(tmp, son);
34         sum += x;
35         d[son] = max(d[son], x);
36     }
37     d[son] = max(d[son], n-sum);
38     if(d[son]<mi)
39     mi = d[son];
40     return sum;
41 }
42 int main()
43 {
44     int i, f;
45     while(~scanf("%d", &n))
46     {
47         memset(e, 0, sizeof(e));
48         memset(head, -1, sizeof(head));
49         memset(vis, 0, sizeof(vis));
50         memset(d, 0, sizeof(d));
51         t = 0;
52         mi = INF;
53 
54         for(i = 1; i < n; i++)
55         {
56             int u, v;
57             scanf("%d%d", &u, &v);
58             add(u, v);
59             add(v, u);
60         }
61         dfs(1, -1);  //把给的树看成以1为根节点。
62 
63         f = 0;
64         for(i = 1; i <= n; i++)
65         {
66            if(d[i]==mi)
67            {
68                if(f)
69                printf(" %d", i);
70                else
71                printf("%d", i);
72                f = 1;
73            }
74         }
75         printf("\n");
76     }
77     return 0;
78 }