poj 3107 删点最大分支最小

http://poj.org/problem?id=3107

这实际上就是找重心，在之前有做过：http://www.cnblogs.com/qlky/p/5780933.html

#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("!
")
#define MAXN 110000+5
#define MAX(a,b) a>b?a:b
#define blank pf("
")
#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

int n,m;

struct node{int y,val,next;}tree[MAXN<<2];

int head[MAXN],vis[MAXN],ptr=1,dp[MAXN],num[MAXN],ans,tot,a[MAXN];

void init()
{
    mem(head,-1);
    mem(vis,0);
    mem(dp,0);
    ans =INF;
    tot = 0;
    ptr=1;
}
void add(int x,int y)
{
    tree[ptr].y = y;
    tree[ptr].next = head[x];
    head[x] = ptr++;
}

void dfs(int rt)
{
    num[rt]=vis[rt]=1;
    int tmp = 0;
    //pf("rt%d
",rt);
    for(int i = head[rt];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(vis[y]) continue;
        dfs(y);
        num[rt]+=num[y];
        tmp = max(tmp,num[y]);
        //pf("y%d %d
",y,tmp);
    }
    tmp = max(tmp,n-num[rt]);
    //pf("t%d %d %d
",rt,tmp,ans);
    if(tmp<ans)
    {
        ans = tmp;
        tot = 0;
        a[tot++] = rt;
    }
    else if(tmp == ans) a[tot++] = rt;
}

int main()
{
    int i,j,k,t;
    while(~sf("%d",&n))
    {
        init();
        for(i=1;i<n;i++)
        {
            int x,y;
            sf("%d%d",&x,&y);
            add(x,y);
            add(y,x);
        }
        dfs(1);
        sort(a,a+tot);
        pf("%d",a[0]);
        for(i=1;i<tot;i++) pf(" %d",a[i]);
        blank;
    }
}