bzoj 1131: [POI2008]Sta

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstdlib>
 4 #include<algorithm>
 5 #include<cmath>
 6 #include<cstring>
 7 #define inf 1000000000
 8 #define ll long long 
 9 using namespace std;
10 int read()
11 {
12     int x=0,f=1;char ch=getchar();
13     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
14     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
15     return x*f;
16 }
17 ll f[1000005];
18 int n,cnt,ans;
19 int last[1000005],deep[1000005],size[1000005];
20 struct edge{int to,next;}e[2000005];
21 void insert(int u,int v)
22 {
23     e[++cnt].to=v;e[cnt].next=last[u];last[u]=cnt;
24     e[++cnt].to=u;e[cnt].next=last[v];last[v]=cnt;
25 }
26 void dfs1(int x,int fa)
27 {
28     size[x]=1;
29     f[x]=deep[x];
30     for(int i=last[x];i;i=e[i].next)
31         if(e[i].to!=fa)
32         {
33             deep[e[i].to]=deep[x]+1;
34             dfs1(e[i].to,x);
35             f[x]+=f[e[i].to];
36             size[x]+=size[e[i].to];
37         }
38 }
39 void dfs2(int x,int fa)
40 {
41     for(int i=last[x];i;i=e[i].next)
42         if(e[i].to!=fa)
43         {
44             f[e[i].to]=f[x]+n-2*size[e[i].to];
45             dfs2(e[i].to,x);    
46         }
47 }
48 int main()
49 {
50     n=read();
51     for(int i=1;i<n;i++)
52     {
53         int a=read(),b=read();
54         insert(a,b);
55     }
56     dfs1(1,0);
57     dfs2(1,0);
58     for(int i=1;i<=n;i++)
59         if(f[i]>f[ans])ans=i;
60     printf("%d",ans);
61     return 0;
62 }