class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        int left = 0;
        int right = letters.size() - 1;
        int mid;

        while(left <= right){
            mid = left + (right - left) / 2;
            if(letters[mid] <= target){
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }

        return left == letters.size() ? letters[0] : letters[left];
    }
};