744. Find Smallest Letter Greater Than Target

class Solution {
    public char nextGreatestLetter(char[] letters, char target) {
        // sanity check 
        if(letters[letters.length - 1] <= target ) return letters[0];
        int left = 0;
        int right = letters.length - 1;
        while(left < right){
            int mid = left + (right - left) / 2;
            if(letters[mid] <= target){
                left = mid + 1;
            }else {
                right = mid;
            }
        }
        return letters[left];
    }
}

一开始这个规则没看到，

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

把规则都弄清楚后， 还是走例子， 

 

 

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'.

Examples:

Input:
letters = ["c", "f", "j"]
target = "a"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "c"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "d"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "g"
Output: "j"

Input:
letters = ["c", "f", "j"]
target = "j"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "k"
Output: "c"