LRU -Cache
"""
The below code provides an implementation
for a Least Recently Used (LRU) cache.
An LRU cache:
1. discards the least recently used item if cache is full
2. places a new item at the front of the cache
3. returns a requested item and then places it at front of cache.
Time complexity: O(1) for put and get methods
Space complexity: O(capacity of LRU cache)
"""
from collections import OrderedDict
class LRUCache(OrderedDict):
# Initialize capacity of cache
def __init__(self, capacity):
self.capacity = capacity
# Get the item associated with key
def get(self, key):
if key not in self:
return - 1
# Move requested item to front of cache
self.move_to_end(key, last=False)
return self[key]
def put(self, key, value):
# Insert/Update item
self[key] = value
# Move new item to front of cache
self.move_to_end(key, last=False)
# Apply cache eviction policy
# Removing the item at end of cache
# i.e., the least recently used item
if len(self) > self.capacity:
self.popitem()
cache = LRUCache(2)
cache.put("First item", 1)
cache.put("Second item", 2)
# Cache content: "Second item": 2, "First item": 1
print(cache.get("First item")) # 1
# Cache content: "First item": 1, "Second item": 2
cache.put("Third item", 3)
# Cache content: "Third item": 3, "First item": 1
print(cache.get("Second item")) # -1
Wissam