【树的重心】 POJ 1655 Balancing Act

求树的重心。。。根据树的重心的定义，使用一遍DFS就行了。。。

#include <iostream>  
#include <queue>  
#include <stack>  
#include <map>  
#include <set>  
#include <bitset>  
#include <cstdio>  
#include <algorithm>  
#include <cstring>  
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 20005
#define maxm 40005
#define eps 1e-10
#define mod 10000007
#define INF 1e9
#define lowbit(x) (x&(-x))
#define mp make_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R  
typedef long long LL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='\n')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
//head

int h[maxn], next[maxm], v[maxm];
int son[maxn], vis[maxn];
int n, ans, mi, cnt;

void init(void)
{
	mi = INF, cnt = 0;
	memset(h, -1, sizeof h);
	memset(vis, 0, sizeof vis);
}
void addedges(int a, int b)
{
	next[cnt] = h[a], h[a] = cnt, v[cnt] = b, cnt++;
}
void read(void)
{
	int a, b;
	scanf("%d", &n);
	for(int i = 1; i < n; i++) {
		scanf("%d%d", &a, &b);
		addedges(a, b);
		addedges(b, a);
	}
}
void dfs(int u)
{
	int t = 0;
	son[u] = 0;
	for(int e = h[u]; ~e; e = next[e]) if(!vis[v[e]]) {
		vis[v[e]] = 1, dfs(v[e]);
		son[u] += son[v[e]] + 1;
		t = max(t, son[v[e]] + 1);
	}
	t = max(t, n - son[u] - 1);
	if(t < mi || (t == mi && ans < u)) mi = t, ans = u;
}
void work(void)
{
	vis[1] = 1, dfs(1);
	printf("%d %d\n", ans, mi);
}
int main(void)
{
	int _;
	while(scanf("%d", &_)!= EOF) {
		while(_--) {
			init();
			read();
			work();
		}
	}
	return 0;
}