Practice/Bloomberg/Leetcode 1472. Design Browser History

Leetcode 1472. Design Browser History

CodingMust

Problem

Design a system to manage video watching history for a streaming platform. Users need the ability to track which videos they've watched and navigate backward and forward through their viewing timeline, similar to how web browsers handle page navigation.

Your task is to implement a TimelineNavigator class that manages this viewing history with the following capabilities:

• Initialize the navigator with a starting video URL (homepage)
• Watch a new video, which adds it to the history
• Navigate backward through previously watched videos
• Navigate forward through videos (only if we've gone back previously)
• Retrieve the currently selected video

A critical behavior: when a user watches a new video after navigating backward, all forward history is erased. This mimics real-world navigation where taking a new action eliminates alternative future paths.

Requirements

1. Implement the TimelineNavigator class with a constructor that accepts an initial video URL
2. Implement watch(url) which navigates to a new video and removes any forward history
3. Implement back(steps) which moves backward up to the specified number of steps (limited by available history) and returns the resulting current video
4. Implement forward(steps) which moves forward up to the specified number of steps (limited by available forward history) and returns the resulting current video
5. Implement current() which returns the URL of the currently selected video
6. Handle edge cases where requested steps exceed available history in either direction

Constraints

• 1 ≤ homepage.length ≤ 100
• 1 ≤ url.length ≤ 100
• 1 ≤ steps ≤ 100
• At most 5000 total operations will be called
• All URLs consist of lowercase English letters, digits, '.', and '/'

Examples

Example 1:

` Operations: navigator = TimelineNavigator("homepage.mp4") navigator.watch("video1.mp4") navigator.watch("video2.mp4") navigator.back(1) navigator.current()

Output: "video1.mp4"

Explanation: Start at homepage.mp4 Watch video1.mp4 (history: [homepage, video1]) Watch video2.mp4 (history: [homepage, video1, video2]) Go back 1 step (now at video1) Current video is video1.mp4 `

Example 2:

` Operations: navigator = TimelineNavigator("start.mp4") navigator.watch("next.mp4") navigator.back(1) navigator.watch("different.mp4") navigator.forward(1) navigator.current()

Output: "different.mp4"

Explanation: Start at start.mp4 Watch next.mp4 (history: [start, next]) Go back 1 step (now at start) Watch different.mp4 (history: [start, different], forward history cleared) Try to go forward 1 step (no forward history exists, stay at different) Current video is different.mp4 `

Example 3:

` Operations: navigator = TimelineNavigator("home.mp4") navigator.watch("a.mp4") navigator.watch("b.mp4") navigator.back(5) navigator.current()

Output: "home.mp4"

Explanation: History: [home, a, b], currently at index 2 Request to go back 5 steps, but only 2 steps available Move back to index 0 (home.mp4) `