线性最长cover（无讲解）

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int maxn=1E6+5;
 4 int n,f[maxn],cover[maxn],R[maxn];
 5 char str[maxn];
 6 int main()
 7 {
 8     ios::sync_with_stdio(false);
 9     cin>>n;
10     for(int i=1;i<=n;++i)
11         cin>>str[i];
12     int pos=0;
13     for(int i=2;i<=n;++i)
14     {
15         while(pos&&str[pos+1]!=str[i])
16             pos=f[pos];
17         if(str[pos+1]==str[i])
18             ++pos;
19         f[i]=pos;
20     }
21     for(int i=1;i<=n;++i)
22     {
23         if(f[i]==0)
24             cover[i]=R[i]=i;
25         else
26         {
27             if(R[cover[f[i]]]+cover[f[i]]>=i)
28             {
29                 cover[i]=cover[f[i]];
30                 R[cover[i]]=i;
31             }
32             else
33                 cover[i]=R[i]=i;
34         }
35     }
36     for(int i=1;i<=n;++i)
37         cout<<cover[i]<<" ";
38     cout<<endl;
39     return 0;
40 }
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k长cover？fail树上k级祖先，长剖即可。