0744. Find Smallest Letter Greater Than Target

# 744. Find Smallest Letter Greater Than Target#

## 题目 #

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.

## 题目大意 #

1. letters长度范围在[2, 10000]区间内。
2. letters 仅由小写字母组成，最少包含两个不同的字母。
3. 目标字母target 是一个小写字母。

## 解题思路 #

• 给出一个字节数组，在这个字节数组中查找在 target 后面的第一个字母。数组是环形的。
• 这一题也是二分搜索的题目，先在数组里面查找 target，如果找到了，取这个字母的后一个字母。如果没有找到，就取 low 下标的那个字母。注意数组是环形的，所以最后结果需要对下标取余。

## 代码 #

``````
package leetcode

func nextGreatestLetter(letters []byte, target byte) byte {
low, high := 0, len(letters)-1
for low <= high {
mid := low + (high-low)>>1
if letters[mid] > target {
high = mid - 1
} else {
low = mid + 1
}
}
find := letters[low%len(letters)]
if find <= target {
return letters[0]
}
return find
}

``````

Apr 8, 2023