线性最长cover（无讲解）

 #include<bits/stdc++.h>
 using namespace std;
 const int maxn=1E6+;
 int n,f[maxn],cover[maxn],R[maxn];
 char str[maxn];
 int main()
 {
     ios::sync_with_stdio(false);
     cin>>n;
     for(int i=;i<=n;++i)
         cin>>str[i];
     int pos=;
     for(int i=;i<=n;++i)
     {
         while(pos&&str[pos+]!=str[i])
             pos=f[pos];
         if(str[pos+]==str[i])
             ++pos;
         f[i]=pos;
     }
     for(int i=;i<=n;++i)
     {
         if(f[i]==)
             cover[i]=R[i]=i;
         else
         {
             if(R[cover[f[i]]]+cover[f[i]]>=i)
             {
                 cover[i]=cover[f[i]];
                 R[cover[i]]=i;
             }
             else
                 cover[i]=R[i]=i;
         }
     }
     for(int i=;i<=n;++i)
         cout<<cover[i]<<" ";
     cout<<endl;
     return ;
 }

k长cover？fail树上k级祖先，长剖即可。