[leetcode]744. Find Smallest Letter Greater Than Target大于Target的最小字母

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.

题意

Solution1

code

 1 class Solution {
 2     public char nextGreatestLetter(char[] letters, char target) {
 3         
 4         if (letters[0] > target) return letters[0];
 5         if (letters[letters.length - 1] <= target) return letters[0];
 6         
 7         int left = 0;
 8         int right = letters.length - 1;
 9         while (left <= right) {
10             int mid = left + (right - left) / 2;
11             if (letters[mid] <= target) {
12                 left = mid + 1;
13             }
14             else if (letters[mid] > target) {
15                 right = mid - 1;
16             }
17         }
18         return letters[left];    
19     }
20 }