P4323 [JSOI2016]独特的树叶（树哈希）

传送门

树哈希？->这里
反正大概就是乱搞……的吧……

//minamoto
#include<bits/stdc++.h>
#define R register
#define ll long long
#define fp(i,a,b) for(R int i=a,I=b+1;i<I;++i)
#define fd(i,a,b) for(R int i=a,I=b-1;i>I;--i)
#define go(u) for(int i=head[u],v=e[i].v;i;i=e[i].nx,v=e[i].v)
template<class T>inline bool cmin(T&a,const T&b){return a>b?a=b,1:0;}
template<class T>inline bool cmax(T&a,const T&b){return a<b?a=b,1:0;}
using namespace std;
char buf[1<<21],*p1=buf,*p2=buf;
inline char getc(){return p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++;}
int read(){
    R int res,f=1;R char ch;
    while((ch=getc())>'9'||ch<'0')(ch=='-')&&(f=-1);
    for(res=ch-'0';(ch=getc())>='0'&&ch<='9';res=res*10+ch-'0');
    return res*f;
}
const int N=1e5+5,Base=998244353,P=1e9+7;
struct eg{int v,nx;}e[N<<1];int head[N],tot;bool is;
int n,m,f[N],fa[N],g[N],bin[N],sz[N],deg[N],ans=P,u,v;
vector<int>son[N],sl[N],sr[N];set<int>vis;
inline void add(R int u,R int v){if(is)++deg[v];e[++tot]={v,head[u]},head[u]=tot;}
int dfs1(int u,int fat){
	sz[u]=1,fa[u]=fat,vector<int>().swap(son[u]);
	go(u)if(v!=fat)son[u].push_back(dfs1(v,u)),sz[u]+=sz[v];
	if(son[u].empty())return f[u]=1;sort(son[u].begin(),son[u].end());
	ll res=0;fp(i,0,son[u].size()-1)res=(res*Base+son[u][i])%P;
	return f[u]=sz[u]*res%P;
}
void dfs2(int u){
	if(fa[u])son[u].push_back(g[u]),sort(son[u].begin(),son[u].end());
	int Sz=son[u].size();sl[u].resize(Sz),sl[u][0]=son[u][0];
	fp(i,1,Sz-1)sl[u][i]=(1ll*sl[u][i-1]*Base+son[u][i])%P;
	sr[u].resize(Sz),sr[u][Sz-1]=son[u][Sz-1];
	fd(i,Sz-2,0)sr[u][i]=(sr[u][i+1]+1ll*son[u][i]*bin[Sz-i-1])%P;
	go(u)if(v!=fa[u]){
		if(Sz==1){g[v]=1,dfs2(v);break;}
		int p=lower_bound(son[u].begin(),son[u].end(),f[v])-son[u].begin();
		g[v]=0;if(p+1<Sz)g[v]=sr[u][p+1];
		if(p-1>=0)g[v]=(g[v]+1ll*sl[u][p-1]*bin[Sz-1-p])%P;
		g[v]=1ll*g[v]*(n-sz[v])%P;
		if(is&&deg[v]==1&&vis.find(g[v])!=vis.end())cmin(ans,v);
		dfs2(v);
	}if(!is)vis.insert(1ll*sl[u][Sz-1]*n%P);
}
int main(){
//	freopen("testdata.in","r",stdin);
	bin[0]=1;fp(i,1,N-1)bin[i]=1ll*bin[i-1]*Base%P;
	n=read();fp(i,1,n-1)u=read(),v=read(),add(u,v),add(v,u);
	dfs1(1,0),dfs2(1),tot=0,is=1,++n;memset(head,0,sizeof(head));
	fp(i,1,n-1)u=read(),v=read(),add(u,v),add(v,u);
	dfs1(1,0);if(deg[1]==1&&vis.find(f[e[head[1]].v])!=vis.end())ans=1;
	else dfs2(1);printf("%d
",ans);return 0;
}