LeetCode:744. 尋找比目標字母大的最小字母

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        letters.push_back(letters[0]);
        if(target!='z')
        {
            for(int i=0;i<letters.size();i++)
            {
                if(letters[i]>target)
                {
                    return letters[i];
                }
            }
            return letters[0];
        }
        else
        {
            return letters[0];
        }
        return ' ';
    }
};