【bzoj4401】块的计数

#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
using namespace std;
 
#define N 1000010
 
struct edge
{
    int to,next;
}e[N<<1];
int head[N<<1];
int cnt;
 
int n;
int x,y;
int ans;
 
int f[N],p[N];
 
void link(int x,int y)
{
    e[++cnt]=(edge){y,head[x]};
    head[x]=cnt;
}
 
void dfs(int x,int d)
{
    f[x]=1;
    for (int i=head[x];i;i=e[i].next)
        if (e[i].to!=d)
        {
            dfs(e[i].to,x);
            f[x]+=f[e[i].to];
        }
    p[f[x]]++;
}
 
int main()
{
    scanf("%d",&n);
    for (int i=1;i<n;i++)
        scanf("%d%d",&x,&y),link(x,y),link(y,x);
    dfs(1,0);
    for (int i=1;i<=n;i++)
    {
        for (int j=i<<1;j<=n;j+=i)
            p[i]+=p[j];
        if (i*p[i]==n)
            ans++;
    }
    printf("%d",ans);
    return 0;
}