POJ 1655 Balancing Act（树的重心）

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #define lli long long int 
 6 using namespace std;
 7 const int MAXN=2000001;
 8 const int maxn=0x7fffff;
 9 void read(int &n)
10 {
11     char c=‘+‘;int x=0;bool flag=0;
12     while(c<‘0‘||c>‘9‘){c=getchar();if(c==‘-‘)flag=1;}
13     while(c>=‘0‘&&c<=‘9‘)
14     x=(x<<1)+(x<<3)+c-48,c=getchar();
15     flag==1?n=-x:n=x;
16 }
17 struct node
18 {
19     int u,v,w,nxt;
20 }edge[MAXN];
21 int head[MAXN];
22 int num=1;
23 int size[MAXN];
24 int ans=maxn;
25 int out=maxn;
26 int n;
27 int mx[MAXN];
28 void add_edge(int x,int y)
29 {
30     edge[num].u=x;
31     edge[num].v=y;
32     edge[num].nxt=head[x];
33     head[x]=num++;
34 }
35 void dfs(int pos,int fa)
36 {
37 //    cout<<pos<<endl;
38     size[pos]=1;
39     int now=0;
40     for(int i=head[pos];i!=-1;i=edge[i].nxt)
41     {
42         
43         if(edge[i].v!=fa)
44         {
45             dfs(edge[i].v,pos);
46             size[pos]+=size[edge[i].v];
47             mx[pos]=max(mx[pos],size[edge[i].v]);
48         }
49     }
50     mx[pos]=max(mx[pos],n-size[pos]);
51     if(mx[pos]<mx[ans])
52         ans=pos;
53     if(mx[pos]==mx[ans]&&pos<ans)
54         ans=pos;
55 }
56 int  main()
57 {
58     int T;
59     read(T);
60     while(T--)
61     {
62         read(n);
63         //cout<<maxn<<endl;
64         num=1;
65         memset(head,-1,sizeof(head));
66         memset(size,0,sizeof(size));
67         memset(mx,0,sizeof(mx));
68         mx[0]=maxn;
69         ans=0;
70         for(int i=1;i<=n-1;i++)
71         {
72             int x,y,z;
73              read(x);read(y);
74              add_edge(x,y);
75              add_edge(y,x);
76         }
77         dfs(1,0);
78         printf("%d %d\n",ans,mx[ans]);    
79         
80     } 
81     return 0;
82 }