poj 3107 树重心

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <cctype>
#include <vector>
#include <iterator>
#include <set>
#include <map>
#include <sstream>
using namespace std;

#define mem(a,b) memset(a,b,sizeof(a))
#define pf printf
#define sf scanf
#define spf sprintf
#define pb push_back
#define debug printf("!\n")
#define MAXN 50000+5
#define MAX(a,b) a>b?a:b
#define blank pf("\n")
#define LL long long
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define pqueue priority_queue
#define INF 0x3f3f3f3f

#define ls (rt<<1)
#define rs (rt<<1|1)

int n,m;

int ptr = 1,head[MAXN],vis[MAXN];

int res,ans[MAXN],son[MAXN],num=0;

struct node
{
    int y,val,next;
}tree[MAXN<<1];

void add(int fa,int son)
{
    tree[ptr].y = son;
    tree[ptr].next = head[fa];
    head[fa] = ptr++;
}

void dfs(int root)
{
    vis[root] = 1;
    son[root] = 0;
    int tmp = 0;
    for(int i=head[root];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(vis[y]) continue;
        dfs(y);
        son[root] += son[y]+1;
        tmp = max(son[y]+1,tmp);
    }
    tmp = max(tmp,n-son[root]-1);
    if(tmp<res)
    {
        ans[0] = root;
        num = 1;
        res = tmp;
    }
    else if(tmp == res) ans[num++] = root;
}


int main()
{
    int i,j,t,kase=1;
    while(~sf("%d",&n))
    {
        mem(tree,0);
        mem(head,-1);
        mem(vis,0);
        mem(ans,0);
        res=INF;
        ptr = 1;
        num = 0;
        int x,y;
        for(i=1;i<n;i++)
        {
            sf("%d%d",&x,&y);
            add(x,y);
            add(y,x);
        }
        dfs(1);
        sort(ans,ans+num);
        pf("%d",ans[0]);
        for(i=1;i<num;i++) pf(" %d",ans[i]);
        blank;
    }
    return 0;
}