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=0;int res;
    while(!isdigit(ch=getchar()))
    (ch=='-')&&(flag=true);
    for(res=num;isdigit(ch=getchar());res=res*10+num);
    (flag)&&(res=-res);
    #undef num
    return res;
}
template<class T>inline bool cmax(T&a,const T&b){return a<b?a=b,1:0;}
const int N=1e5+5;
char str[N],s[N];
ll ans=0;
int ver[N],Next[N],head[N],tot=0;
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][26],fa[N],l[N],cnt[N];
    int s[N],tag[N],son[N][26],le[N];
    SAM(){rt=last=tot=1;}
    int ins(int c){
        int p=last,np=++tot;last=np,le[np]=l[np]=l[p]+1,cnt[np]=1;
        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]+1) fa[np]=q;
            else{
                int nq=++tot;
                memcpy(ch[nq],ch[q],sizeof(ch[q]));
                l[nq]=l[p]+1,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=1;i<=tot;++i) ++c[l[i]];
        for(int i=1;i<=tot;++i) c[i]+=c[i-1];
        for(int i=tot;i;--i) a[c[l[i]]--]=i;
        for(int i=tot,p;i>=2;--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=0;
        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+1);
        }
    }
    inline void push(){for(int i=1;i<=tot;++i) tag[a[i]]+=tag[fa[a[i]]];}
}sam1,sam2;
void findrt(int u,int fa){
    sz[u]=1,son[u]=0;
    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=0,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=1;i<=sam1.tot;++i) sam1.tag[i]=0;
    for(int i=1;i<=sam2.tot;++i) sam2.tag[i]=0;
    int to=str[fa]-'a';
    if(fa) sam1.mark(u,fa,sam1.son[1][to],1),sam2.mark(u,fa,sam2.son[1][to],1);
    else sam1.mark(u,fa,1,0),sam2.mark(u,fa,1,0);
    sam1.push(),sam2.push();
    for(int i=1;i<=m;++i) ans+=1ll*op*sam1.tag[id1[i]]*sam2.tag[id2[m-i+1]];
}
void solve(int u){
    if(size<=sqr){
        num=0,get(u,0);
        for(int i=1;i<=num;++i) dfs(g[i],0,sam1.rt);
        return;
    }
    vis[u]=1,work(u,0,1);
    for(int i=head[u];i;i=Next[i])
    if(!vis[ver[i]]) work(ver[i],u,-1);
    for(int i=head[u];i;i=Next[i]){
        int v=ver[i];
        if(vis[v]) continue;
        size=0,getsum(v,u);
        rt=0,findrt(v,u);
        solve(rt);
    }
}
int main(){
//    freopen("testdata.in","r",stdin);
    n=read(),m=read();
    for(int i=1,u,v;i<n;++i)
    u=read(),v=read(),add(u,v),add(v,u);
    scanf("%s",str+1),scanf("%s",s+1);
    for(int i=1;i<=m;++i) sam1.s[i]=s[i]-'a',id1[i]=sam1.ins(s[i]-'a');
    reverse(s+1,s+1+m);
    for(int i=1;i<=m;++i) sam2.s[i]=s[i]-'a',id2[i]=sam2.ins(s[i]-'a');
    sam1.calc(),sam2.calc();
    rt=0,son[0]=n+1,size=n,sqr=sqrt(n);
    findrt(1,0),solve(rt);
    printf("%lld\n",ans);
    return 0;
}