POJ 1655 Balancing Act 树的重心 基础题

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 
 5 using namespace std;
 6 
 7 const int maxn=20000+5;
 8 const int inf=0x3f3f3f3f;
 9 
10 struct Edge
11 {
12     int to,next;
13 }edge[maxn<<1];
14 
15 int head[maxn];
16 int tot;
17 int son[maxn];
18 int siz[maxn];
19 int ans[maxn];
20 
21 void init()
22 {
23     memset(head,-1,sizeof(head));
24     tot=1;
25     memset(ans,0,sizeof(ans));
26     memset(son,-1,sizeof(son));
27 }
28 
29 void addedge(int u,int v)
30 {
31     edge[tot].to=v;
32     edge[tot].next=head[u];
33     head[u]=tot++;
34 }
35 
36 void dfs(int u,int fa)
37 {
38     siz[u]=1;
39     for(int i=head[u];~i;i=edge[i].next)
40     {
41         int v=edge[i].to;
42         if(v==fa)
43             continue;
44         dfs(v,u);
45         siz[u]+=siz[v];
46         if(son[u]==-1||siz[v]>siz[son[u]])
47             son[u]=v;
48     }
49 }
50 
51 int solve(int n)
52 {
53     dfs(1,-1);
54 
55     for(int i=1;i<=n;i++)
56         ans[i]=max(siz[son[i]],n-siz[i]);
57     int id=1;
58     for(int i=2;i<=n;i++)
59     {
60         if(ans[i]<ans[id])
61             id=i;
62     }
63     return id;
64 }
65 
66 int main()
67 {
68     int test;
69     scanf("%d",&test);
70     while(test--)
71     {
72         int n;
73         scanf("%d",&n);
74         init();
75 
76         for(int i=1;i<n;i++)
77         {
78             int u,v;
79             scanf("%d%d",&u,&v);
80             addedge(u,v);
81             addedge(v,u);
82         }
83 
84         int id=solve(n);
85 
86         printf("%d %d\n",id,ans[id]);
87     }
88 
89     return 0;
90 }