Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.
Implement the LRUCache class:
LRUCache(int capacity) Initialize the LRU cache with 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 key.
The functions get and put must each run in O(1) average time complexity.
Example 1:
Input
["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"]
[[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]
Output
[null, null, null, 1, null, -1, null, -1, 3, 4]
Explanation
LRUCache lRUCache = new LRUCache(2);
lRUCache.put(1, 1); // cache is {1=1}
lRUCache.put(2, 2); // cache is {1=1, 2=2}
lRUCache.get(1); // return 1
lRUCache.put(3, 3); // LRU key was 2, evicts key 2, cache is {1=1, 3=3}
lRUCache.get(2); // returns -1 (not found)
lRUCache.put(4, 4); // LRU key was 1, evicts key 1, cache is {4=4, 3=3}
lRUCache.get(1); // return -1 (not found)
lRUCache.get(3); // return 3
lRUCache.get(4); // return 4
Constraints:
1 <= capacity <= 30000 <= key <= 1040 <= value <= 105- At most
2 * 105 calls will be made to get and put.
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class Node():
def __init__(self, key, val):
self.key = key
self.val = val
self.prev = None
self.next = None
class LRUCache:
def __init__(self, capacity: int):
self.cache = {}
self.size = 0
self.capacity = capacity
self.head = Node(0, 0)
self.tail = Node(0, 0)
self.head.next = self.tail
self.tail.prev = self.head
def _add_node(self, node):
# add to head
node.prev = self.head
node.next = self.head.next
self.head.next.prev = node
self.head.next = node
def _remove_node(self, node):
# remove from tail
prev_node = node.prev
next_node = node.next
prev_node.next = next_node
next_node.prev = prev_node
def _move_to_head(self, node):
self._remove_node(node)
self._add_node(node)
def _pop_tail(self):
node = self.tail.prev
self._remove_node(node)
return node
def get(self, key: int) -> int:
node = self.cache.get(key, None)
if not node:
return -1
self._move_to_head(node)
return node.val
def put(self, key: int, value: int) -> None:
node = self.cache.get(key)
if not node:
new_node = Node(key, value)
self.cache[key] = new_node
self._add_node(new_node)
self.size += 1
if self.size > self.capacity:
tail = self._pop_tail()
del self.cache[tail.key]
self.size -= 1
else:
node.val = value
self._move_to_head(node)
# Your LRUCache object will be instantiated and called as such:
# obj = LRUCache(capacity)
# param_1 = obj.get(key)
# obj.put(key,value)
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