杭电多校第一场 —— Distinct Sub-palindromes

题意：给出一个字符串的长度，要求求出字符串的回文子串数量（不重复）
思路：写出n = 1, n = 2, n = 3发现规律res = 26^n, 当n >= 4时，res均等于A(3, 26) 选择三个字符进行排列 ： "abca", "abcab", "abcabc" …………
代码()：

#pragma GCC optimize(2)
#include<bits/stdc++.h>
#define lowbit(n) n & (-n)
#define mem(a) memset(a, 0, sizeof(a));
#define Buff ios::sync_with_stdio(false)
#define sqr(x) x*x
#define pb push_back
#define x first
#define y second
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int>PII;
const int mod = 1e9 + 7;
const double eps = 1e-6;
const int base = 131;
const int N = 1e6+7;
int main()
{
    int T;
    cin >> T;
    while(T --)
    {
        int n;
        cin >> n;
        if(n == 1)                    cout << 26 <<endl;
        else if(n == 2)               cout << 26 * 26 <<endl;
        else  if(n == 3)              cout << 26 * 26 * 26 <<endl;
        else                          cout << 26 * 25 * 24 << endl;
    }
    return 0;
}