Similarity of Subtrees（深搜+hash、映射）

map<ULL,LL>mp;
vector<int>g
;
ULL dp
;
LL ans;int n;
const ULL b=1000000007;
void dfs(int u,int fa){
dp[u]=1;
for(int i=0;i<g[u].size();++i){
int v=g[u][i];
if(v==fa)continue;
dfs(v,u);
dp[u]+=dp[v]*b;
}
ans+=mp[dp[u]];
mp[dp[u]]++;
}
int main(){
sf("%d",&n);
ans=0;
rep(i,1,n-1){
int u,v;sf("%d%d",&u,&v);
g[u].push_back(v);g[v].push_back(u);
}
dfs(1,1);
cout<<ans<<'\n';
}