LeetCode 744 - Find Smallest Letter Greater Than Target

https://leetcode.com/problems/find-smallest-letter-greater-than-target/description/

Given a list of sorted characters letters containing only lowercase letters, and given a target letter target, find the smallest element in the list that is larger than the given target.

Letters also wrap around. For example, if the target is target = 'z' and letters = ['a', 'b'], the answer is 'a'.

    public char nextGreatestLetter(char[] letters, char target) {

        int lo = 0, hi = letters.length;

        while (lo < hi) {

            int mi = lo + (hi - lo) / 2;

            if (letters[mi] <= target) lo = mi + 1;

            else hi = mi;

        }

        return letters[lo % letters.length];

    }

    public char nextGreatestLetter(char[] letters, char target) {
        for (char c: letters)
            if (c > target) return c;
        return letters[0];
    }


    public char nextGreatestLetter(char[] letters, char target) {
        boolean[] seen = new boolean[26];
        for (char c: letters)
            seen[c - 'a'] = true;

        while (true) {
            target++;
            if (target > 'z') target = 'a';
            if (seen[target - 'a']) return target;
        }
    }