744. Find Smallest Letter Greater Than Target

Posted 2020-10-18 __Meng

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):

 1 class Solution {
 2 public:
 3     char nextGreatestLetter(vector<char>& letters, char target) {
 4         int left = 0 ;
 5         int right = letters.size() - 1 ;
 6         while(left < right){
 7             int mid = (left+right)>>1 ;
 8             if (target < letters[mid])
 9                 right = mid ;
10             else
11                 left = mid + 1 ;
12         }
13         return target < letters[left] ? letters[left] : letters[0] ;
14     }
15 };