leetcode 744. Find Smallest Letter Greater Than Target-蒲公英云

leetcode 744. Find Smallest Letter Greater Than Target

https://leetcode.com/problems/find-smallest-letter-greater-than-target/

给定一个元素已经排好序的字符数组以及一个目标字符，找到第一个大于目标字符的元素并返回

一、问题分析

测试用例如下：

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"

其中需要注意的是，当target大于字符数组所有元素时，返回字符数组的首元素

二、代码实现

class Solution {
    public char nextGreatestLetter(char[] letters, char target) {
        int left = 0, right = letters.length - 1;
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (letters[mid] > target) {
                if (mid == 0 || letters[mid - 1] <= target) {
                    return letters[mid];
                }
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        if (letters[left] > target) {
            return letters[left];
        }
        //letters[left] 一定小于等于 target
        return letters[0];
    }
}