Find Smallest Letter Greater than Target

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"

 

Note:

1. letters has a length in range [2, 10000].
2. letters consists of lowercase letters, and contains at least 2 unique letters.
3. target is a lowercase letter.

 

class Solution {
    public char nextGreatestLetter(char[] letters, char target) {
        int low = 0, high = letters.length - 1;
        char letter = '~';
        while (low <= high) {
            int mid = low + (high - low) / 2;
            if (letters[mid] > target) {
                if (letters[mid] > target) {
                    letter = letters[mid];
                }
                high = mid - 1;
            } else {
                low = mid + 1;
            }
        }
        
        return letter == '~' ? letters[0] : letter;
    }
}