题目
题解

#include<bits/stdc++.h>
using namespace std;
const int N=100001;
map<int,int>mp[N];
map<vector<int>,int>H;
set<int>S;
vector<int>e[N];
int n,i,x,y,tot;
inline char gc(){
	static char buf[100000],*p1=buf,*p2=buf;
	return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;
}
inline int rd(){
	int x=0,fl=1;char ch=gc();
	for (;ch<48||ch>57;ch=gc())if(ch=='-')fl=-1;
	for (;48<=ch&&ch<=57;ch=gc())x=(x<<3)+(x<<1)+(ch^48);
	return x*fl;
}
inline void wri(int a){if(a<0)a=-a,putchar('-');if(a>=10)wri(a/10);putchar(a%10|48);}
inline void wln(int a){wri(a);puts("");}
int dfs(int u,int fa){
	vector<int>cnt;
	if (mp[u][fa]) return mp[u][fa];
	for (int i=0,v;i<e[u].size();i++)
		if ((v=e[u][i])!=fa) cnt.push_back(dfs(v,u));
	sort(cnt.begin(),cnt.end());
	if (!H[cnt]) H[cnt]=++tot;
	return mp[u][fa]=H[cnt];
}
int main(){
	n=rd();
	for (i=1;i<n;i++) x=rd(),y=rd(),e[x].push_back(y),e[y].push_back(x);
	for (i=1;i<=n;i++)
		if (e[i].size()<4) S.insert(dfs(i,0));
	printf("%d",S.size());
}