static public char nextGreatestLetter(char[] letters, char target) {
        int[] a = new int[26];
        int min = 0;
        for (int i = 0; i < letters.length; i++) {
            a[letters[i] - 'a']++;
        }
        for (int i = target - 'a' + 1; i < a.length; i++) {
            if (a[i] != 0)
                return (char) (i + 'a');
        }
        for (int i = 0; i < a.length; i++) {
            if (a[i] != 0)
                return (char) (i + 'a');
        }
        return '0';
    }
Why Did you create this class? what does it do?
src/problems/easy/FindSmallestLetterGreaterThanTarget.java