POJ 3107 Godfather

求树的重心。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxv 50050
#define maxe 100500
using namespace std;
struct edge
{
    int v,nxt;
}e[maxe];
struct pnt
{
    int id,val;
}p[maxv];
int n,x,y,g[maxv],nume=0,size[maxv];
bool cmp(pnt x,pnt y)
{
    if (x.val!=y.val) return x.val<y.val;
    return x.id<y.id;
}
void addedge(int u,int v)
{
    e[++nume].v=v;
    e[nume].nxt=g[u];
    g[u]=nume;
}
void dfs(int x,int fath)
{
    size[x]=1;int ret=-0;
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=fath)
        {
            dfs(v,x);
            size[x]+=size[v];
            ret=max(ret,size[v]);
        }
    }
    ret=max(n-size[x],ret);
    p[x].id=x;p[x].val=ret;
}
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n-1;i++)
    {
        scanf("%d%d",&x,&y);
        addedge(x,y);
        addedge(y,x);
    }
    dfs(1,1);
    sort(p+1,p+n+1,cmp);
    int pp=1;
    printf("%d ",p[pp].id);
    while (p[pp+1].val==p[pp].val)    
    {
        printf("%d ",p[pp+1].id);
        pp++;
    }
    printf("\n");
    return 0;
}