BZOJ 3238 [Ahoi2013]差异 ——后缀自动机

后缀自动机的parent树就是反串的后缀树。

所以只需要反向构建出后缀树，就可以乱搞了。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define F(i,j,k) for (int i=j;i<=k;++i)
#define D(i,j,k) for (int i=j;i>=k;--i)
#define ll long long
#define maxn 1000005
 
struct sam{
    ll ans;
    char s[maxn];
    int cnt,last,siz[maxn],len;
    int go[maxn][26],fa[maxn],l[maxn];
    int h[maxn],to[maxn],ne[maxn],en;
    void addedge(int a,int b)
    {to[en]=b;ne[en]=h[a];h[a]=en++;}
    void init()
    {
        cnt=last=1;
        memset(go,0,sizeof go);
    }
    void add(int x)
    {
//      printf("add %d\n",x);
        int p=last,np=last=++cnt;l[np]=l[p]+1;//printf("np is %d\n",np);
        for (;p&&!go[p][x];p=fa[p]) go[p][x]=np;
        if (!p) fa[np]=1;
        else
        {
            int q=go[p][x];
            if (l[q]==l[p]+1) fa[np]=q;
            else
            {
                int nq=++cnt; l[nq]=l[p]+1; //printf("nq is %d\n",nq);
                memcpy(go[nq],go[q],sizeof go[q]);
                fa[nq]=fa[q];
                fa[np]=fa[q]=nq;
                for (;p&&go[p][x]==q;p=fa[p]) go[p][x]=nq;
            }
        }
        siz[np]=1;
//      printf("siz %d is %d\n",np,1);
    }
    void read()
    {
        scanf("%s",s+1); len=strlen(s+1);
        D(i,len,1) add(s[i]-'a');
    }
    void dfs(int o)
    {
//      printf("dfs on %d len is %d\n",o,l[o]);
        for (int i=h[o];i>=0;i=ne[i])
        {
             
            dfs(to[i]);
//          printf("%d & %d -= %lld\n",o,to[i],(ll)2*siz[o]*siz[to[i]]*l[o]);
            ans-=(ll)2*siz[o]*siz[to[i]]*l[o];
            siz[o]+=siz[to[i]];
        }
    }
    void work()
    {
        ans=(ll)(len-1)*(len+1)*len/2;
        dfs(1);
        printf("%lld\n",ans);
    }
    void build()
    {
        en=0;
        memset(h,-1,sizeof h);
        F(i,1,cnt) addedge(fa[i],i);
    }
}SAM;
 
int main()
{
    SAM.init();
    SAM.read();
    SAM.build();
    SAM.work();
}