How do you solve Greatest English Letter in Upper and Lower Case on LeetCode?

Greatest English Letter in Upper and Lower Case (LeetCode #2309) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Using a set allows for O(1) average time complexity for lookups.

What is the time complexity of Greatest English Letter in Upper and Lower Case?

The optimal solution for Greatest English Letter in Upper and Lower Case runs in O(n) time and uses O(n) space. This complexity is efficient because we only iterate through the string once to build the set, and then we check the alphabet in constant time.

What is the brute force solution for Greatest English Letter in Upper and Lower Case?

The brute force approach for Greatest English Letter in Upper and Lower Case is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach checks each letter in the string to see if it has both uppercase and lowercase versions. This is a straightforward method but can be inefficient for longer strings. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Greatest English Letter in Upper and Lower Case?

Greatest English Letter in Upper and Lower Case uses the following concepts: Hash Table, String, Enumeration. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Greatest English Letter in Upper and Lower Case?

Always clarify the problem requirements before jumping into coding. Think about edge cases, such as strings with no matching letters. Explain your thought process as you code; it helps the interviewer understand your approach.

What are common mistakes when solving Greatest English Letter in Upper and Lower Case?

Not considering the case sensitivity properly. Forgetting to check both cases before adding to the result.

#2309

Greatest English Letter in Upper and Lower Case

Easy

Hash TableStringEnumerationHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

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Intuition

Time O(n)Space O(n)

The optimal approach utilizes a set to track the characters seen in the string, allowing for efficient lookups. By iterating in reverse order (from 'Z' to 'A'), we can directly find the greatest letter that appears in both cases.

⚙️

Algorithm

4 steps

1Step 1: Create a set to store all characters in the string.
2Step 2: Iterate through the alphabet from 'Z' to 'A'.
3Step 3: For each letter, check if both the uppercase and lowercase versions are in the set.
4Step 4: Return the first letter found or an empty string if none exist.

solution.py8 lines

1# Full working Python code
2
3def greatestLetter(s):
4    seen = set(s)
5    for c in range(ord('Z'), ord('A') - 1, -1):
6        if chr(c) in seen and chr(c + 32) in seen:
7            return chr(c)
8    return ''

ℹ

Complexity note: This complexity is efficient because we only iterate through the string once to build the set, and then we check the alphabet in constant time.

1Using a set allows for O(1) average time complexity for lookups.
2Iterating in reverse order ensures we find the greatest letter first.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.