744. Find Smallest Letter Greater Than Target

Easy
​
You are given an array of characters letters that is sorted in non-decreasing order, and a character target. There are at least two different characters in letters.
Return the smallest character in letters that is lexicographically greater than target. If such a character does not exist, return the first character in letters.
Example 1:
Input: letters = ["c","f","j"], target = "a"
Output:
"c"
Explanation:
The smallest character that is lexicographically greater than 'a' in letters is 'c'.
Example 2:
Input: letters = ["c","f","j"], target = "c"
Output:
"f"
Explanation:
The smallest character that is lexicographically greater than 'c' in letters is 'f'.
Example 3:
Input: letters = ["x","x","y","y"], target = "z"
Output:
"x"
Explanation:
There are no characters in letters that is lexicographically greater than 'z' so we return letters[0].
Constraints:
  • 2 <= letters.length <= 104
  • letters[i] is a lowercase English letter.
  • letters is sorted in non-decreasing order.
  • letters contains at least two different characters.
  • target is a lowercase English letter.

解題

O(n) 暴力解
func nextGreatestLetter(letters []byte, target byte) byte {
ans := byte('|')
​
for _, letter := range letters {
if letter > target && letter < ans {
ans = letter
}
}
​
if ans == byte('|') { return letters[0] }
​
return ans
}