LRU cache design with hash map and doubly linked list in Data Structures Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the role of the hash map in LRU cache

In an LRU cache implemented with a hash map and a doubly linked list, what is the primary purpose of the hash map?

A To store the order of usage of cache items

B To provide fast access to cache items by key

C To remove the least recently used item from the cache

D To maintain the size limit of the cache

💡 Hint

Think about how you find an item quickly by its key.

The hash map allows quick lookup of cache items by their keys, enabling O(1) access time. The doubly linked list manages the order of usage.

🧠 Conceptual

intermediate

Purpose of the doubly linked list in LRU cache

Why is a doubly linked list used in an LRU cache alongside a hash map?

A To quickly find cache items by key

B To store the cache items in sorted order by key

C To maintain the order of items from most to least recently used

D To limit the cache size automatically

💡 Hint

Consider how the cache knows which item to remove when full.

The doubly linked list keeps track of the usage order, allowing quick updates when items are accessed or removed, supporting O(1) insertion and deletion.

🔍 Analysis

advanced

Effect of accessing a cache item on the doubly linked list

In an LRU cache, when a cache item is accessed, what change happens to the doubly linked list?

A The accessed item is moved to the front of the list

B The accessed item is moved to the end of the list

C The accessed item is removed from the list

D No change happens to the list

💡 Hint

Think about which item should be considered most recently used after access.

Accessing an item updates its usage status, so it is moved to the front of the doubly linked list to mark it as most recently used.

❓ Reasoning

advanced

Why does the LRU cache remove the tail node when full?

When the LRU cache reaches its capacity and needs to add a new item, why is the tail node of the doubly linked list removed?

A Because the tail node is the least recently used item

B Because the tail node is the most recently used item

C Because the tail node is the largest key value

D Because the tail node is the oldest inserted item regardless of usage

💡 Hint

Consider which item should be discarded to make space.

The tail node represents the least recently used item, so removing it frees space for new items while preserving the most recently used ones.

❓ Comparison

expert

Comparing time complexities of operations in LRU cache

Which statement correctly compares the time complexities of the main operations (get and put) in an LRU cache implemented with a hash map and doubly linked list?

A Get runs in O(n) time, but put runs in O(1) time

B Get runs in O(1) time, but put runs in O(n) time due to list updates

C Both get and put operations run in O(n) time because of list traversal

D Both get and put operations run in O(1) time due to hash map and linked list usage

💡 Hint

Think about how the hash map and doubly linked list work together to optimize operations.

The hash map provides O(1) access to nodes, and the doubly linked list allows O(1) insertion and deletion, so both get and put run in constant time.