poj 1655 Balancing Act 寻找树的重心

就是寻找树的重心的果题。

http://poj.org/problem?id=1655

#include <map>
#include <set>
#include <queue>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>

using namespace std;

const int MAXN = 20005;
const int MAXE = 40005;

int N;

struct Edge {
    int to;
    Edge * next;
}*EE,E[MAXE];

struct Gragh{
    Edge * first;
}G[MAXN];

int tot;
int siz[MAXN];//有多少个子节点
int num[MAXN];//子树中最大的
int root;

void init() {
    EE = E;
    memset(E,0,sizeof(E));
    memset(G,0,sizeof(G));
    num[root=0] = N;
}

void addedge(int u,int v) {
    EE->to = v; EE->next = G[u].first; G[u].first = EE++;
    EE->to = u; EE->next = G[v].first; G[v].first = EE++;
}

void dfs(int u,int fa = 0) {
    siz[u] = 1;
    num[u] = 0;
    for(Edge * p = G[u].first ; p ; p = p -> next) {
        if(p->to != fa) {
            dfs(p->to,u);
            siz[u] += siz[p->to];
            num[u] = max(num[u],siz[p->to]);
        }
    }
    num[u] = max(N-siz[u],num[u]);
    if(num[u] < num[root]) root = u;
}

void input() {
    scanf("%d",&N);
    init();
    int u,v;
    for(int i = 1 ; i <= N - 1 ; i++) {
        scanf("%d %d",&u,&v);
        addedge(u,v);
    }
}

void solve() {
    dfs(1);
    printf("%d %d\n",root,num[root]);
}

int main(void) {
    //freopen("a.in","r",stdin);
    int T;
    scanf("%d",&T);
    while(T--) {
        input();
        solve();
    }
    return 0;
}