Build a least-recently-used cache

LRU Cache Implementation

Design and implement a data structure for a Least Recently Used (LRU) cache. It should support the following operations: get and put.

• LRUCache(int capacity): Initialize the LRU cache with a 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 item.

Both get and put must run in O(1) average time complexity.

Constraints

• 1 <= capacity <= 3000
• 0 <= key <= 10^4
• 0 <= value <= 10^5

Example

# Initialize with capacity 2
lru = LRUCache(2)
lru.put(1, 1)
lru.put(2, 2)
lru.get(1)    # returns 1
lru.put(3, 3) # evicts key 2
lru.get(2)    # returns -1 (not found)
lru.put(4, 4) # evicts key 1
lru.get(1)    # returns -1
lru.get(3)    # returns 3
lru.get(4)    # returns 4

Implementation Template

class LRUCache:
    def __init__(self, capacity: int):
        pass

    def get(self, key: int) -> int:
        pass

    def put(self, key: int, value: int) -> None:
        pass