Longest Substring with K Unique Characters | Brute Force + Sliding Window (Python, C++, Java)
In this video, we solve the important sliding window problem Longest Substring with K Unique Characters.
We begin with the brute force approach to understand how substrings are generated and checked, and then move to the optimized sliding window technique to achieve better performance.
You will learn:
How to track unique characters in a substring
Brute force approach and why it is inefficient
Optimized sliding window using hashmap/set
How to handle exactly K unique characters
Two pointers (left and right) technique
Time complexity improvement from O(n²) to O(n)
Clean and interview-ready code in Python, C++, and Java
This problem is a must-do to master sliding window patterns and is frequently asked in interviews, especially for understanding substring constraints.
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