Solution

All Implemented Interfaces:
```
public final class Solution

                    
```
2309 - Greatest English Letter in Upper and Lower Case.
Easy
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"
Explanation:
The letter 'E' is the only letter to appear in both lower and upper case.
Example 2:
Input: s = "arRAzFif"
Output: "R"
Explanation:
The letter 'R' is the greatest letter to appear in both lower and upper case.
Note that 'A' and 'F' also appear in both lower and upper case, but 'R' is greater than 'F' or 'A'.
Example 3:
Input: s = "AbCdEfGhIjK"
Output: ""
Explanation: There is no letter that appears in both lower and upper case.
Constraints:
- 1 <= s.length <= 1000
- s consists of lowercase and uppercase English letters.

Nested Class Summary

Nested Classes
Modifier and Type	Class	Description

Field Summary

Fields
Modifier and Type	Field	Description

Constructor Summary

Constructors
Constructor	Description
`Solution()`

Enum Constant Summary

Enum Constants
Enum Constant	Description

Method Summary

Modifier and Type	Method	Description
`final String`	`greatestLetter(String s)`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail
- Solution
```
Solution()
```

Method Detail
- greatestLetter
```
 final String greatestLetter(String s)
```