线性最长cover（无讲解）

#include<bits/stdc++.h>
using namespace std;
const int maxn=1E6+5;
int n,f[maxn],cover[maxn],R[maxn];
char str[maxn];
int main()
{
    ios::sync_with_stdio(false);
    cin>>n;
    for(int i=1;i<=n;++i)
        cin>>str[i];
    int pos=0;
    for(int i=2;i<=n;++i)
    {
        while(pos&&str[pos+1]!=str[i])
            pos=f[pos];
        if(str[pos+1]==str[i])
            ++pos;
        f[i]=pos;
    }
    for(int i=1;i<=n;++i)
    {
        if(f[i]==0)
            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=1;i<=n;++i)
        cout<<cover[i]<<" ";
    cout<<endl;
    return 0;
}

k长cover？fail树上k级祖先，长剖即可。