P3146 [USACO16OPEN]248

 1 #include<iostream>
 2 #include<cstring>
 3 #include<cstdlib>
 4 #include<cstdio>
 5 #include<algorithm>
 6 #include<cmath>
 7 using namespace std;
 8 int n,m,ans;
 9 int f[270000][66],a[270000];
10 int main(){
11     scanf("%d",&n);
12     for (int i=1;i<=n;i++){
13         scanf("%d",&a[i]);
14         f[i][a[i]]=i+1;
15     }
16     for (int j=2;j<=60;j++)
17         for (int i=1;i<=n;i++){
18             if (f[i][j]==0) f[i][j]=f[f[i][j-1]][j-1];
19             if (f[i][j]>0) ans=max(ans,j);
20         }
21     printf("%d\n",ans);
22     return 0;
23 }