Problem Description

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.

Implement the LRUCache class:

• LRUCache(int capacity) Initialize the LRU cache with positive size capacity.
• int get(int key) Return the value of the key if the key exists, otherwise return -1.
• void put(int key, int value) Update the value of the key if the key exists. Otherwise, add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation, evict the least recently used key.

The functions get and put must each run in O(1) average time complexity.

Approach

We can combine a Hash Map (for O(1) lookups) and a Doubly Linked List (for O(1) removals and additions).

• Node class to hold key, value, prev, next
• Head and Tail dummy nodes in the Doubly Linked List to ease boundary operations.

Solution

// Add your implementation here...
class LRUCache {

    public LRUCache(int capacity) {
        
    }
    
    public int get(int key) {
        return -1;
    }
    
    public void put(int key, int value) {
        
    }
}