hdu multi-school (one) 1004 (sign in)

1004 Distinct Sub-palindromes (sign in)

Meaning of the title: the given length is nnstringSS of$n$$S$ , the task is to outputtheSSwith the least number ofdifferentsub-palindromesThe number of$S$
Ideas:
At first I thought it was a dp push sequence, combinatorics started...
But when I pushed it by hand, it seemed like a simple sign-in question. First,
find the sequence with the fewest sub-palindromes.

• $n=1$ : 26 letters
• $n=2$：$26^2$（$aa$俩:$a,a$ ;$ab$俩:$a,b$）
• $n=3$：$26^3$ (Push it by yourself and found that you can put it anywhere, the number of different sub-palindromes is 3)
• $n\ge 4:A_3^{26}=26\ast 25\ast 24$ , Choose any three different letters and arrange them in the specified order (ex: abcabc), the number of different sub-palindromes is 3.
  Code:

int main() {
    
    
    LL t, n;
    LL ans = 0;
    cin >> t;
    while (t--)
    {
    
    
        cin >> n;
        if (n <= 3) {
    
    
            cout << qpow(26, n) << endl;
        }
        else
        {
    
    
            ans = (26 * 25 * 24) % MOD;
            cout << ans << endl;
        }

    }
    return 0;
    
}