Java · Coding problem

Recently Viewed Items

A free coding problem from the Java 21: Sequenced Collections and the Rest of 18-21 skill. Read it here, then solve it in the app in Java.

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  • Easy
  • Coding problem
  • Free
  • Java

The problem

An online store in Portland shows each shopper the items they viewed recently. Write RecentlyViewed:

  • view(item): the item becomes the most recent. Viewing an item that's already in the list moves it to the front (no duplicates). Keep at most capacity items, dropping the least recent.
  • recent(): the items, most recent first, as a list the caller can't use to change this object (later views must not change a list already handed out, and changing that list must not change this object).
  • oldest(): the least recently viewed item, or none if nothing has been viewed yet.
  • oldestFirst(): the items, least recent first.

Java 21's sequenced collections make each of these a single call on the right collection.

Example

Input:  3
        view shoes
        view hat
        view scarf
        view shoes
        recent
        oldest
        oldestFirst
Output: recent: [shoes, scarf, hat]
        oldest: hat
        oldest first: [hat, scarf, shoes]

Constraints

  • 1 <= capacity <= 50
  • up to 100 commands

How it's graded

  • Run checks your code against the examples. Submit also runs hidden tests, and you see pass or fail for them, never their inputs.
  • Stuck? Hints come in four steps, from a nudge to a code skeleton, each costing part of the points.
  • Once you pass, you see the approaches from brute force to optimal, and where your solution lands among them.

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