Greatest English Letter in Upper and Lower Case
Given a string of English letters s, return the greatest English letter which occurs as both a lowercase and uppercase letter in s. The returned letter should be in uppercase. If no such letter exists, return an empty string.
An English letter b is greater than another letter a if b appears after a in the English alphabet.
Example 1
Input
s = "lEeTcOdE"Output
"E"The letter 'E' is the only letter to appear in both lower and upper case.
Example 2
Input
s = "arRAzFif"Output
"R"The letter 'R' is the greatest letter to appear in both lower and upper case; 'A' and 'F' also appear in both lower and upper case, but 'R' is greater than both.
Constraints
- 1 <= s.length <= 1000
- s consists of lowercase and uppercase English letters.