洛谷P3804 后缀自动机

 

先贴板子,留坑

#include<bits/stdc++.h>
#define ll long long
#define IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define rep(ii,a,b) for(int ii=a;ii<=b;++ii)
#define per(ii,a,b) for(int ii=b;ii>=a;--ii)
using namespace std;//head
const int maxn=2e6+10,maxm=27+10;
int casn,n,m,k;
namespace sam{
int fa[maxn<<1],son[maxn<<1][maxm],len[maxn<<1];
int last,cnt,t[maxn],val[maxn],num[maxn],a[maxn];
  void insert(int ch){
    int pos=last,npos=++cnt;
    last=npos,len[npos]=len[pos]+1;
    for(;pos&&!son[pos][ch];pos=fa[pos]) son[pos][ch]=npos;
    if(!pos) fa[npos]=1;
    else {
      int q=son[pos][ch];
      if(len[pos]+1==len[q]) fa[npos]=q;
      else {
        int nq=++cnt;len[nq]=len[pos]+1;
        memcpy(son[nq],son[q],sizeof(son[q]));
        fa[nq]=fa[q];fa[q]=fa[npos]=nq;
        for(;son[pos][ch]==q;pos=fa[pos]) son[pos][ch]=nq;
      }
    }
    val[npos]=1;
  }
  void makesam(char *s,int len){
    last=cnt=1;rep(i,1,len) insert(s[i]-'a');
  }
  ll getans(){
    ll ans=0;
    rep(i,1,cnt)++num[len[i]];
    rep(i,1,cnt)num[i]+=num[i-1];
    rep(i,1,cnt)a[num[len[i]]--]=i;
    per(i,1,cnt){
      int pos=a[i];val[fa[pos]]+=val[pos];
      if(val[pos]>1) ans=max(ans,1ll*val[pos]*len[pos]);
    }
    return ans;
  }
}
char s[maxn];
int main(){IO;
  cin>>(s+1);n=strlen(s+1);
  sam::makesam(s,n);
  cout<<sam::getans()<<endl;
}