1. # 运用你所掌握的数据结构，设计和实现一个 LRU (最近最少使用) 缓存机制 。
    2. #
    3. #
    4. #
    5. #  实现 LRUCache 类：
    6. #
    7. #
    8. #  LRUCache(int capacity) 以正整数作为容量 capacity 初始化 LRU 缓存
    9. #  int get(int key) 如果关键字 key 存在于缓存中，则返回关键字的值，否则返回 -1 。
    10. #  void put(int key, int value) 如果关键字已经存在，则变更其数据值；如果关键字不存在，则插入该组「关键字-值」。当缓存容量达到上
    11. # 限时，它应该在写入新数据之前删除最久未使用的数据值，从而为新的数据值留出空间。
    12. #
    13. #
    14. #
    15. #
    16. #
    17. #
    18. #  进阶：你是否可以在 O(1) 时间复杂度内完成这两种操作？
    19. #
    20. #
    21. #
    22. #  示例：
    23. #
    24. #
    25. # 输入
    26. # ["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"]
    27. # [[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]
    28. # 输出
    29. # [null, null, null, 1, null, -1, null, -1, 3, 4]
    30. #
    31. # 解释
    32. # LRUCache lRUCache = new LRUCache(2);
    33. # lRUCache.put(1, 1); // 缓存是 {1=1}
    34. # lRUCache.put(2, 2); // 缓存是 {1=1, 2=2}
    35. # lRUCache.get(1);    // 返回 1
    36. # lRUCache.put(3, 3); // 该操作会使得关键字 2 作废，缓存是 {1=1, 3=3}
    37. # lRUCache.get(2);    // 返回 -1 (未找到)
    38. # lRUCache.put(4, 4); // 该操作会使得关键字 1 作废，缓存是 {4=4, 3=3}
    39. # lRUCache.get(1);    // 返回 -1 (未找到)
    40. # lRUCache.get(3);    // 返回 3
    41. # lRUCache.get(4);    // 返回 4
    42. #
    43. #
    44. #
    45. #
    46. #  提示：
    47. #
    48. #
    49. #  1 <= capacity <= 3000
    50. #  0 <= key <= 3000
    51. #  0 <= value <= 104
    52. #  最多调用 3 * 104 次 get 和 put
    53. #
    54. #  Related Topics 设计
    55. #  👍 1039 👎 0
    58. # leetcode submit region begin(Prohibit modification and deletion)
    59. class Node(object):
    60.     def __init__(self, key=0, value=0):
    61.         self.key = key
    62.         self.value = value
    63.         self.pre = None
    64.         self.next = None
    67. class LRUCache(object):
    69.     def __init__(self, capacity):
    70.         """
    71.         :type capacity: int
    72.         """
    73.         self.cache = dict()
    74.         self.capacity = capacity
    75.         self.size = 0
    76.         self.head = Node()
    77.         self.tail = Node()
    78.         self.head.next = self.tail
    79.         self.tail.pre = self.head
    81.     def get(self, key):
    82.         """
    83.         :type key: int
    84.         :rtype: int
    85.         """
    86.         if key in self.cache:
    87.             node = self.cache[key]
    88.             self.moveToHead(node)
    89.             return node.value
    90.         else:
    91.             return -1
    93.     def put(self, key, value):
    94.         """
    95.         :type key: int
    96.         :type value: int
    97.         :rtype: None
    98.         """
    99.         if key in self.cache:
    100.             node = self.cache[key]
    101.             node.value = value
    102.             self.moveToHead(node)
    103.         else:
    104.             node = Node(key, value)
    105.             self.cache[key] = node
    106.             self.addToHead(node)
    107.             self.size += 1
    108.             if self.size > self.capacity:
    109.                 removed = self.removeTail()
    110.                 self.cache.pop(removed.key)
    111.                 self.size -= 1
    113.     def addToHead(self, node):
    114.         node.pre = self.head
    115.         node.next = self.head.next
    116.         self.head.next.pre = node
    117.         self.head.next = node
    119.     def removeNode(self, node):
    120.         node.pre.next = node.next
    121.         node.next.pre = node.pre
    123.     def moveToHead(self, node):
    124.         self.removeNode(node)
    125.         self.addToHead(node)
    127.     def removeTail(self):
    128.         node = self.tail.pre
    129.         self.removeNode(node)
    130.         return node
    133. # Your LRUCache object will be instantiated and called as such:
    134. # obj = LRUCache(capacity)
    135. # param_1 = obj.get(key)
    136. # obj.put(key,value)
    137. # leetcode submit region end(Prohibit modification and deletion)
    139. obj = LRUCache(2)
    140. obj.put(1, 1)
    141. obj.put(2, 2)
    142. obj.get(1)
    143. obj.put(3, 3)
    144. print(obj.get(2))