Approach: Sliding Window with HashSet To solve this problem efficiently, we can use a sliding window approach with a HashSet to track unique characters. Initialize Two Pointers: left pointer to track the start of the window. right pointer to expand the window. A HashSet to store the characters in the current window. Expand the Window: Move the right pointer to add characters to the window. If the character is already in the set, shrink the window from the left until the duplicate character is removed. Update the maximum length: At each step, update max_length if the current window is the longest found so far.