LeetCode exercise 387, "First Unique Character in a String," is a classic problem with a staggering 2.8 million total submissions and 1.7 million accepted solutions. This immense popularity makes it one of the most frequently attempted exercises on the platform.

Why a Frequency Array Approach?

Even though numerous solutions exist for LeetCode 387, delving into alternative approaches like the frequency array offers several benefits:

• Deeper Understanding: Exploring different approaches deepens your understanding of the problem itself. By analyzing the problem from multiple perspectives, you gain a more comprehensive grasp of its underlying mechanics.

• Expanded Toolkit: Each new approach you learn adds to your algorithmic toolbox, equipping you with a wider range of tools to tackle similar challenges in the future.

• Unique Insights: The frequency array approach offers a distinct perspective compared to the more common hashmap-based solutions. By utilizing an array to track character frequencies, you gain insights into a different way of solving string manipulation problems.

Frequency Array Approach in Action:

Here's a breakdown of the frequency array approach:

1. Frequency Array:

   • An integer array freqArray of size 26 is created to store the frequency of each character (a-z).

   • The base variable is set to the ASCII value of 'a' for easy character position calculation.

2. Counting Frequencies:

   • The code iterates over the string using an enhanced for loop.

   • Each character c is converted to its integer position in the freqArray and the corresponding frequency count is incremented.

3. Finding the Unique Character:

   • A second loop iterates over the string again.

   • For each character c, its position in the freqArray is calculated.

   • If the frequency at that position is 1, it means the character appears only once, and its index is returned.

   • If no unique character is found, -1 is returned.

Key Points:

• Efficient Approach: This approach has a time complexity of O(n) and space complexity of O(1) (assuming the input string contains only lowercase letters), making it efficient for solving this problem.

• Clarity: The use of an enhanced for loop and clear variable naming enhance the code's readability.

Learning Approach:

• Starting with Hashmaps: It's perfectly normal to start with hashmap-based approaches for similar problems. Exploring different solutions like this frequency array approach helps you expand your problem-solving toolkit.

• Understanding the Strategy: Focusing on understanding the underlying strategy behind each approach is crucial. This allows you to apply the concepts to similar problems in the future.

• Testing and Refinement: Using LeetCode test cases to refine your solution ensures its correctness and helps you identify potential edge cases.

Further Exploration:

• Recording a Video: Consider recording a video explaining this exercise step-by-step. This can help showcase your understanding and assist others in learning from your approach.

• Practicing Different Techniques: By understanding this frequency array approach and practicing with different techniques, you can effectively tackle various string manipulation problems on LeetCode and beyond.

Fun Fact:

Did you know that when you would make a new leetcode account in June 2024 you would be ranking around 5,000,000 so even if we would only have 1,000,000 distinct people how have successfully solved this exercise it is still quite impressive because for example exercise 50 from leetcoe has 4.8M submissions and the same amouont of accepted exercises