洛谷P4218 [CTSC2010]珠宝商（后缀自动机+点分治）

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这题思路太清奇了……->题解

 //minamoto
 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<cmath>
 #define ll long long
 using namespace std;
 inline int read(){
     #define num ch-'0'
     char ch;bool flag=;int res;
     while(!isdigit(ch=getchar()))
     (ch=='-')&&(flag=true);
     for(res=num;isdigit(ch=getchar());res=res*+num);
     (flag)&&(res=-res);
     #undef num
     return res;
 }
 template<class T>inline bool cmax(T&a,const T&b){return a<b?a=b,:;}
 const int N=1e5+;
 char str[N],s[N];
 ll ans=;
 int ver[N],Next[N],head[N],tot=;
 int sqr,id1[N],id2[N];
 inline void add(int u,int v){
     ver[++tot]=v,Next[tot]=head[u],head[u]=tot;
 }
 int vis[N],rt,son[N],sz[N],size,n,m;
 struct SAM{
     int rt,last,tot,ch[N][],fa[N],l[N],cnt[N];
     int s[N],tag[N],son[N][],le[N];
     SAM(){rt=last=tot=;}
     int ins(int c){
         int p=last,np=++tot;last=np,le[np]=l[np]=l[p]+,cnt[np]=;
         for(;p&&!ch[p][c];p=fa[p]) ch[p][c]=np;
         if(!p) fa[np]=rt;
         else{
             int q=ch[p][c];
             if(l[q]==l[p]+) fa[np]=q;
             else{
                 int nq=++tot;
                 memcpy(ch[nq],ch[q],sizeof(ch[q]));
                 l[nq]=l[p]+,le[nq]=le[q];
                 fa[nq]=fa[q],fa[q]=fa[np]=nq;
                 for(;p&&ch[p][c]==q;p=fa[p]) ch[p][c]=nq;
             }
         }
         return last;
     }
     int a[N],c[N];
     void calc(){
         for(int i=;i<=tot;++i) ++c[l[i]];
         for(int i=;i<=tot;++i) c[i]+=c[i-];
         for(int i=tot;i;--i) a[c[l[i]]--]=i;
         for(int i=tot,p;i>=;--i){
             p=a[i];
             cnt[fa[p]]+=cnt[p];
             son[fa[p]][s[le[p]-l[fa[p]]]]=p;
         }
     }
     void mark(int u,int fa,int now,int len){
         if(!now) return;
         if(len==l[now]) now=son[now][str[u]-'a'];
         else if(s[le[now]-len]!=str[u]-'a') now=;
         if(!now) return;
         ++tag[now];
         for(int i=head[u];i;i=Next[i]){
             int v=ver[i];
             if(v!=fa&&!vis[v]) mark(v,u,now,len+);
         }
     }
     inline void push(){for(int i=;i<=tot;++i) tag[a[i]]+=tag[fa[a[i]]];}
 }sam1,sam2;
 void findrt(int u,int fa){
     sz[u]=,son[u]=;
     for(int i=head[u];i;i=Next[i]){
         int v=ver[i];
         if(v!=fa&&!vis[v])
         findrt(v,u),sz[u]+=sz[v],cmax(son[u],sz[v]);
     }
     cmax(son[u],size-sz[u]);
     if(!rt||son[u]<son[rt]) rt=u;
 }
 int num=,g[N];
 void get(int u,int fa){
     g[++num]=u;
     for(int i=head[u];i;i=Next[i]){
         int v=ver[i];
         if(v!=fa&&!vis[v]) get(v,u);
     }
 }
 void getsum(int u,int fa){
     ++size;
     for(int i=head[u];i;i=Next[i]){
         int v=ver[i];
         if(v!=fa&&!vis[v]) getsum(v,u);
     }
 }
 void dfs(int u,int fa,int now){
     now=sam1.ch[now][str[u]-'a'];
     if(!now) return;
     ans+=sam1.cnt[now];
     for(int i=head[u];i;i=Next[i]){
         int v=ver[i];
         if(v!=fa&&!vis[v]) dfs(v,u,now);
     }
 }
 void work(int u,int fa,int op){
     for(int i=;i<=sam1.tot;++i) sam1.tag[i]=;
     for(int i=;i<=sam2.tot;++i) sam2.tag[i]=;
     int to=str[fa]-'a';
     if(fa) sam1.mark(u,fa,sam1.son[][to],),sam2.mark(u,fa,sam2.son[][to],);
     else sam1.mark(u,fa,,),sam2.mark(u,fa,,);
     sam1.push(),sam2.push();
     for(int i=;i<=m;++i) ans+=1ll*op*sam1.tag[id1[i]]*sam2.tag[id2[m-i+]];
 }
 void solve(int u){
     if(size<=sqr){
         num=,get(u,);
         for(int i=;i<=num;++i) dfs(g[i],,sam1.rt);
         return;
     }
     vis[u]=,work(u,,);
     for(int i=head[u];i;i=Next[i])
     if(!vis[ver[i]]) work(ver[i],u,-);
     for(int i=head[u];i;i=Next[i]){
         int v=ver[i];
         if(vis[v]) continue;
         size=,getsum(v,u);
         rt=,findrt(v,u);
         solve(rt);
     }
 }
 int main(){
 //    freopen("testdata.in","r",stdin);
     n=read(),m=read();
     for(int i=,u,v;i<n;++i)
     u=read(),v=read(),add(u,v),add(v,u);
     scanf("%s",str+),scanf("%s",s+);
     for(int i=;i<=m;++i) sam1.s[i]=s[i]-'a',id1[i]=sam1.ins(s[i]-'a');
     reverse(s+,s++m);
     for(int i=;i<=m;++i) sam2.s[i]=s[i]-'a',id2[i]=sam2.ins(s[i]-'a');
     sam1.calc(),sam2.calc();
     rt=,son[]=n+,size=n,sqr=sqrt(n);
     findrt(,),solve(rt);
     printf("%lld\n",ans);
     return ;
 }