public static int shortPalindrome(String s) {
            int MOD = 1_000_000_007;
            int n = s.length();
            
            long[] singleCount = new long[26];
            long[][] pairCount = new long[26][26];
            long[] tripletCount = new long[26];
            
            long palindromeCount = 0;

            for (char ch : s.toCharArray()) {
                int charIndex = ch - 'a';

                palindromeCount = (palindromeCount + tripletCount[charIndex]) % MOD;

                for (int i = 0; i < 26; i++) {
                    tripletCount[i] = (tripletCount[i] + pairCount[i][charIndex]) % MOD;
                }

                for (int i = 0; i < 26; i++) {
                    pairCount[i][charIndex] = (pairCount[i][charIndex] + singleCount[i]) % MOD;
                }

                singleCount[charIndex] = (singleCount[charIndex] + 1) % MOD;
            }

            return (int) palindromeCount;
        }