744. 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.

 

二分查找，找到大于给定目标的列表中最小的元素。

 

C++(19ms):

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        int left = 0 ;
        int right = letters.size()-1 ;
        while(left < right){
            int mid = left + (right-left)/2 ;
            if (target < letters[mid])
                right = mid ;
            else
                left = mid + 1 ;
        }
        if (target < letters[left])
            return letters[left] ;
        else
            return letters[0] ;
    }
};