# Leetcode 146. LRU Cache

## 題解

### 雙項鍊錶 + 雜湊表

class DListNode:
    def __init__(self, key: int = -1, val: int = -1, prev = None, next = None):
        self.key = key
        self.val = val
        self.prev = prev
        self.next = next

class DLinkedList:
    def __init__(self):
        self.head = DListNode()
        self.tail = DListNode()
        self.head.next = self.tail
        self.tail.prev = self.head
    
    def insert(self, head: DListNode, node: DListNode, tail: DListNode) -> None:
        head.next = node
        node.prev = head
        node.next = tail
        tail.prev = node
    
    def insertFirst(self, node: DListNode): 
        head = self.head
        tail = self.head.next
        self.insert(head,node,tail)
    
    def insertLast(self, node: DListNode):
        head = self.tail.prev
        tail = self.tail
        self.insert(head,node,tail)
  
    def remove(self, node: DListNode):
        head = node.prev
        tail = node.next
        head.next = tail
        tail.prev = head
        node.prev = None
        node.next = None
  
    def changeToFirst(self, node: DListNode) -> None:
        self.remove(node)
        self.insertFirst(node)
        del node

class LRUCache(DLinkedList):
    def __init__(self, capacity: int):
        super().__init__()
        self.capacity = capacity
        self.current_capacity = 0
        self.hash_map = {}
      
    @property
    def reach_max_capacity(self):
        return self.current_capacity > self.capacity

    def get(self, key: int) -> int:
        if key in self.hash_map:
            node = self.hash_map[key]
            self.changeToFirst(node)
            return node.val
        return -1

    def put(self, key: int, value: int) -> None:
        if key not in self.hash_map:
            node = DListNode(key,value)
            self.insertFirst(node)
            self.hash_map[key] = node
            self.current_capacity += 1
            if self.reach_max_capacity:
                node = self.hash_map[self.tail.prev.key]
                del self.hash_map[node.key]
                self.remove(node)
                del node
                self.current_capacity -= 1
        else:
            node = self.hash_map[key]
            node.val = value
            self.changeToFirst(node)

# Your LRUCache object will be instantiated and called as such:
# obj = LRUCache(capacity)
# param_1 = obj.get(key)
# obj.put(key,value)

## 參考

https://isdaniel.github.io/lru-algorithm/