class Node:
def __init__(self, key=0, val=0):
self.key = key
self.val = val
self.prev = None
self.next = None
class LRUCache:
def __init__(self, capacity):
self.cap = capacity
self.map = {}
self.head = Node()
self.tail = Node()
self.head.next = self.tail
self.tail.prev = self.head
def _remove(self, node):
node.prev.next = node.next
node.next.prev = node.prev
def _addToFront(self, node):
node.next = self.head.next
node.prev = self.head
self.head.next.prev = node
self.head.next = node
def get(self, key):
if key not in self.map:
return -1
node = self.map[key]
self._remove(node)
self._addToFront(node)
return node.val
def put(self, key, value):
if key in self.map:
self._remove(self.map[key])
node = Node(key, value)
self._addToFront(node)
self.map[key] = node
if len(self.map) > self.cap:
lru = self.tail.prev
self._remove(lru)
del self.map[lru.key]
time per operation. space for capacity .