Use a doubly linked list with dummy head/tail sentinels and a hash map from key to node.
class Node:
key, value, prev, next
class LRUCache:
function init(capacity):
self.cap = capacity
self.map = {}
self.head = Node(0, 0)
self.tail = Node(0, 0)
self.head.next = self.tail
self.tail.prev = self.head
function get(key):
if key not in self.map:
return -1
node = self.map[key]
remove(node)
addToHead(node)
return node.value
function put(key, value):
if key in self.map:
remove(self.map[key])
node = Node(key, value)
self.map[key] = node
addToHead(node)
if len(self.map) > self.cap:
lru = self.tail.prev
remove(lru)
del self.map[lru.key]
function remove(node):
node.prev.next = node.next
node.next.prev = node.prev
function addToHead(node):
node.next = self.head.next
node.prev = self.head
self.head.next.prev = node
self.head.next = node
per operation, space.