Design Browser History

Design Browser History

1. What is this problem about?

The Design Browser History interview question asks you to simulate the navigation of a web browser. You start at a home page and can visit new URLs. You must also support back and forward operations, allowing the user to move through their history. If you visit a new URL while having "forward" history, that forward history is cleared. This Design Browser History coding problem is a test of linear sequence management.

2. Why is this asked in interviews?

Cisco and Microsoft use this to test your ability to implement Design interview patterns using simple data structures. It evaluates whether you choose a structure that allows fast movement in both directions and efficient modification. It’s a classic application of Linked List interview patterns or Stack interview patterns.

3. Algorithmic pattern used

• Method 1 (Two Stacks): Use one stack for the "back" history and another for the "forward" history. Visiting a page pushes to "back" and clears "forward."
• Method 2 (Dynamic Array): Use a list and a currentIndex. back and forward just change the index. visit appends a new URL and truncates any elements beyond the current index.
• Method 3 (Doubly-Linked List): Each page is a node. back and forward move the current pointer. visit creates a new node and deletes the next chain.

4. Example explanation

Start at google.com.

1. visit("leetcode.com"): History: [google, leetcode]. Current: leetcode.
2. visit("youtube.com"): History: [google, leetcode, youtube]. Current: youtube.
3. back(1): Current moves to leetcode.
4. visit("facebook.com"): Forward history (youtube) is deleted. History: [google, leetcode, facebook].

5. Common mistakes candidates make

• Memory Management: Forgetting to clear the "forward" history when a new visit occurs.
• Inefficient Truncation: If using a list, manually deleting elements one by one ($O(N)$) instead of using a built-in slicing or range-clear function.
• Pointer Errors: Losing the link to the rest of the list when using a manual node-based structure.

6. Interview preparation tip

The Dynamic Array (ArrayList/Vector) approach is usually the fastest to implement and most memory-efficient for this specific problem. It provides $O(1)$ navigation and $O(1)$ amortized insertion.