744. Find Smallest Letter Greater Than Target -----------E

Q:

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.

A:

一开始没有弄明白什么是wrap around. 下面这个，没有用上 list of sorted characters

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        char largerRes ='A';
        char smallerRes = 'A';
        for(auto ch:letters)
        {
            if(ch>target){
                if( isupper(largerRes) || ch < largerRes )
                {
                    largerRes = ch;
                }
            }else if(ch<target){
                if( isupper(smallerRes) || ch < smallerRes )
                {
                    smallerRes = ch;
                }
            }
        }
        return isupper(largerRes)?smallerRes:largerRes;
    }
};

-----------------------利用了sorted List---

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        for(auto ch:letters)
            if(ch > target)
                return ch;
        return letters[0];
    }
};