744. 尋找比目標字母大的最小字母

二分

難度：簡單
推薦學習視頻：花花醬

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        //2020.2.27 二分 左閉有開
        int n = letters.size();
        int l = 0, r = n;
        while(l < r){
            int mid = l + r >> 1;
            if(letters[mid] <= target) l = mid + 1;
            else r = mid;
        }
        return letters[l%n];
    }
};