【洛谷P3804】后缀自动机

题面

https://www.luogu.org/problem/P3804

题解

// luogu-judger-enable-o2
#include<cstdio>
#include<iostream>
#include<cstring>
#define ri register int
#define N 1000050
using namespace std;

char s[N];
int n;
int ans=0;

struct SAM{
  int ff[N<<1],cnt[N<<1];
  int ch[N<<1][26];
  int len[N<<1];
  int tot,last;
    
  int ton[N<<1],a[N<<1];

  inline void copy(int nq,int q) {
    for (ri i=0;i<26;i++) ch[nq][i]=ch[q][i];
    ff[nq]=ff[q];
  }
  inline void extend(int o) {
    int p=last,np,q,nq;
    np=++tot;
    len[np]=len[p]+1;
    last=np;
    while (p&&!ch[p][o]) ch[p][o]=np,p=ff[p];
    if (!p) ff[np]=1;
    else {
      q=ch[p][o];
      if (len[q]==len[p]+1) ff[np]=q;
      else {
        nq=++tot;
        copy(nq,q);
        len[nq]=len[p]+1;
        ff[np]=ff[q]=nq;
        while (p && ch[p][o]==q) ch[p][o]=nq,p=ff[p];
      }
    }
    cnt[np]=1;
  }

  void work() {
    for (ri i=1;i<=tot;i++) ton[len[i]]++;
    for (ri i=1;i<=n;i++) ton[i]+=ton[i-1];
    for (ri i=1;i<=tot;i++) a[ton[len[i]]--]=i;
    for (ri i=tot;i>=1;i--) cnt[ff[a[i]]]+=cnt[a[i]];
    for (ri i=1;i<=tot;i++) if (cnt[i]>1) ans=max(ans,len[i]*cnt[i]);
  }
} sam;

int main() {
  scanf("%s",s+1);
  n=strlen(s+1);
  sam.tot=1; sam.last=1;
  for (ri i=1;i<=n;i++) sam.extend(s[i]-'a');
  ans=0;
  sam.work();
  printf("%d
",ans);
}