Problem
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 1 1 <= capacity <= 3000 3000 3000
- 0 0 0 <= key <= 1 0 4 10^4 104
- 0 0 0 <= value <= 1 0 5 10^5 105
- At most 2 ? 1 0 5 2 * 10^5 2?105 calls will be made to get and put.
Algorithm
map and doubly linked list.
https://www.code-recipe.com/post/lru-cache
Code
class LRUCache:
def __init__(self, capacity: int):
class node:
def __init__(self, key, val, L=None, R=None):
self.key = key
self.val = val
self.L = L
self.R = R
class dlink:
def __init__(self):
self.head = node(-1, -1)
self.tail = node(-1, -1)
self.head.R = self.tail
self.tail.L = self.head
self.len = 0
def add_node(self, key, val):
new_node = node(key, val, self.head, self.tail)
new_node.L = self.head
new_node.R = self.head.R
self.head.R.L = new_node
self.head.R = new_node
self.len += 1
return new_node
def del_node(self, now_node=None):
if not now_node:
now_node = self.tail.L
now_node.L.R = now_node.R
now_node.R.L = now_node.L
self.len -= 1
return now_node
self.len = capacity
self.map = {}
self.lik = dlink()
def get(self, key: int) -> int:
if key in self.map:
index = self.lik.del_node(self.map[key])
del self.map[index.key]
new_node = self.lik.add_node(index.key, index.val)
self.map[key] = new_node
return new_node.val
return -1
def put(self, key: int, value: int) -> None:
if key in self.map:
self.lik.del_node(self.map[key])
del self.map[key]
new_node = self.lik.add_node(key, value)
self.map[key] = new_node
if len(self.map) > self.len:
now_node = self.lik.del_node() # Remove last node
del self.map[now_node.key]
# Your LRUCache object will be instantiated and called as such:
# obj = LRUCache(capacity)
# param_1 = obj.get(key)
# obj.put(key,value)
