146_LRUCache.py

# 146. LRU Cache
# Neetcode's solution
# Doubly Linked List, Hashmap.

class Node:
    def __init__(self, key, val):
        self.key, self.val  = key, val
        self.prev = self.next = None


class LRUCache:

    def __init__(self, capacity: int):
        self.capacity = abs(capacity)
        self.cache = {}
        
        self.left, self.right = Node(0,0), Node(0,0)
        self.left.next, self.right.prev = self.right, self.left 
        
    def remove(self, node):
        prev, next_ = node.prev, node.next
        prev.next, next_.prev = next_, prev
    
    def insert(self, node):
        prev, next_ = self.right.prev, self.right
        prev.next = next_.prev = node
        node.next, node.prev = next_, prev

    def get(self, key: int) -> int:
        if key in self.cache:
            self.remove(self.cache[key])
            self.insert(self.cache[key])
            return self.cache[key].val
        return -1
        
    def put(self, key: int, value: int) -> None:
        if key in self.cache:
            self.remove(self.cache[key])
        self.cache[key] = Node(key, value)
        self.insert(self.cache[key])
        
        if len(self.cache)>self.capacity:
            lru = self.left.next
            self.remove(lru)
            del self.cache[lru.key]
                


# Your LRUCache object will be instantiated and called as such:
# obj = LRUCache(capacity)
# param_1 = obj.get(key)
# obj.put(key,value)