POJ1655 Balancing Act

题面:http://poj.org/problem?id=1655

本题是求树的重心裸题。

Code:
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<ctime>
using namespace std;
const int N=20005;
int n,f[N],size[N];
struct Node{
    int v,Next;
}Edge[N*2];
int head[N],Cnt;
void Push(int u,int v){
	++Cnt;
    Edge[Cnt].v=v;
    Edge[Cnt].Next=head[u];
    head[u]=Cnt;
}
void dfs(int u,int fa){
	size[u]=1;
    for(int i=head[u];i;i=Edge[i].Next){
        int v=Edge[i].v;
        if(v==fa){
			continue;
		}
        dfs(v,u);
        f[u]=max(f[u],size[v]);
        size[u]+=size[v];
    }
    f[u]=max(f[u],n-size[u]);
}
int main(){
    int t,u,v;
    scanf("%d",&t);
    while(t--){
		memset(head,0,sizeof(head));
		memset(f,0,sizeof(f));
		Cnt=0;
        scanf("%d",&n);
        for(int i=1;i<n;i++){
            scanf("%d%d",&u,&v);
            Push(u,v);
            Push(v,u);
        }
        dfs(1,0);
        int ans1=1,ans2=f[1];
        for(int i=2;i<=n;i++){
            if(ans2>f[i]){
                ans1=i;
                ans2=f[i];
            }
		}
        printf("%d %d\n",ans1,ans2);
    }
    return 0;
}