iframe-proxy | Sunbelt Computer Software

History

195 lines (143 loc) · 4.95 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

from __future__ import annotations

from typing import Callable

class DoubleLinkedListNode:

"""

Double Linked List Node built specifically for LRU Cache

"""

def __init__(self, key: int, val: int):

self.key = key

self.val = val

self.next = None

self.prev = None

class DoubleLinkedList:

"""

Double Linked List built specifically for LRU Cache

"""

def __init__(self):

self.head = DoubleLinkedListNode(None, None)

self.rear = DoubleLinkedListNode(None, None)

self.head.next, self.rear.prev = self.rear, self.head

def add(self, node: DoubleLinkedListNode) -> None:

"""

Adds the given node to the end of the list (before rear)

"""

temp = self.rear.prev

temp.next, node.prev = node, temp

self.rear.prev, node.next = node, self.rear

def remove(self, node: DoubleLinkedListNode) -> DoubleLinkedListNode:

"""

Removes and returns the given node from the list

"""

temp_last, temp_next = node.prev, node.next

node.prev, node.next = None, None

temp_last.next, temp_next.prev = temp_next, temp_last

return node

class LRUCache:

"""

LRU Cache to store a given capacity of data. Can be used as a stand-alone object

or as a function decorator.

>>> cache = LRUCache(2)

>>> cache.set(1, 1)

>>> cache.set(2, 2)

>>> cache.get(1)

>>> cache.set(3, 3)

>>> cache.get(2) # None returned

>>> cache.set(4, 4)

>>> cache.get(1) # None returned

>>> cache.get(3)

>>> cache.get(4)

>>> cache

CacheInfo(hits=3, misses=2, capacity=2, current size=2)

>>> @LRUCache.decorator(100)

... def fib(num):

... if num in (1, 2):

... return 1

... return fib(num - 1) + fib(num - 2)

>>> for i in range(1, 100):

... res = fib(i)

>>> fib.cache_info()

CacheInfo(hits=194, misses=99, capacity=100, current size=99)

"""

# class variable to map the decorator functions to their respective instance

decorator_function_to_instance_map = {}

def __init__(self, capacity: int):

self.list = DoubleLinkedList()

self.capacity = capacity

self.num_keys = 0

self.hits = 0

self.miss = 0

self.cache = {}

def __repr__(self) -> str:

"""

Return the details for the cache instance

[hits, misses, capacity, current_size]

"""

return (

f"CacheInfo(hits={self.hits}, misses={self.miss}, "

f"capacity={self.capacity}, current size={self.num_keys})"

)

def __contains__(self, key: int) -> bool:

"""

>>> cache = LRUCache(1)

>>> 1 in cache

False

>>> cache.set(1, 1)

>>> 1 in cache

True

"""

return key in self.cache

def get(self, key: int) -> int | None:

"""

Returns the value for the input key and updates the Double Linked List. Returns

None if key is not present in cache

"""

if key in self.cache:

self.hits += 1

self.list.add(self.list.remove(self.cache[key]))

return self.cache[key].val

self.miss += 1

return None

def set(self, key: int, value: int) -> None:

"""

Sets the value for the input key and updates the Double Linked List

"""

if key not in self.cache:

if self.num_keys >= self.capacity:

key_to_delete = self.list.head.next.key

self.list.remove(self.cache[key_to_delete])

del self.cache[key_to_delete]

self.num_keys -= 1

self.cache[key] = DoubleLinkedListNode(key, value)

self.list.add(self.cache[key])

self.num_keys += 1

else:

node = self.list.remove(self.cache[key])

node.val = value

self.list.add(node)

@staticmethod

def decorator(size: int = 128):

"""

Decorator version of LRU Cache

"""

def cache_decorator_inner(func: Callable):

def cache_decorator_wrapper(*args, **kwargs):

if func not in LRUCache.decorator_function_to_instance_map:

LRUCache.decorator_function_to_instance_map[func] = LRUCache(size)

result = LRUCache.decorator_function_to_instance_map[func].get(args[0])

if result is None:

result = func(*args, **kwargs)

LRUCache.decorator_function_to_instance_map[func].set(

args[0], result

)

return result

def cache_info():

return LRUCache.decorator_function_to_instance_map[func]

cache_decorator_wrapper.cache_info = cache_info

return cache_decorator_wrapper

return cache_decorator_inner

if __name__ == "__main__":

import doctest

doctest.testmod()

Sunbelt Computer Software

PL/B Language Development and Support

Navigation Menu

Sunbelt Computer Software

PL/B Language Development and Support

FilesExpand file tree

lru_cache.py

Latest commit

History

lru_cache.py

File metadata and controls