Find Smallest Letter Greater Than Target

题目
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'.

答案

class Solution {
    public char nextGreatestLetter(char[] letters, char target) {
        if(target >= letters[letters.length - 1]) return letters[0];
        target++;
        int l = 0, r = letters.length;
        while(l < r) {
            int m = (l + r) / 2;
            if(letters[m] == target) {
                return target;
            }
            else if(letters[m] < target) {
                l = m + 1;
            }
            else {
                r = m;
            }
        }
        return letters[r];
    }
}