Greatest English Letter in Upper and Lower Case
Below is a step-by-step approach and code to find the greatest English letter that occurs as both a lowercase and uppercase letter in the given string s
. If no such letter exists, we’ll return an empty string.
Understanding the Problem
You are given a string s
containing English letters. You need to find the letter that appears in both lowercase and uppercase forms in s
and is the greatest according to the English alphabet. The returned letter should be in uppercase.
Solution Approach
Create a Set of Candidates: Create an empty set to store letters that are found in both lowercase and uppercase forms.
Iterate Through the String: Iterate through the string, checking for letters that appear in both forms. Add such letters to the set.
Find the Greatest Letter: Find the greatest letter from the set.
Return the Result: Return the greatest letter in uppercase or an empty string if no such letter exists.
Here’s the code:
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Key Takeaways
- We have used a set to keep track of letters found in both forms, ensuring uniqueness.
- We have iterated through the string to find such letters, adding them to the set.
- We have used the
max
function to find the greatest letter and returned it in uppercase. - The code handles the case where no such letter is found, returning an empty string.
This code meets the problem’s constraints and provides a clear solution to find the desired letter from the given string.