lru.py

class Node:
    def __init__(self, key, data):
        self.next = None
        self.prev = None
        self.key = key
        self.data = data


class LinkedList:
    def __init__(self):
        self.head = None
        self.tail = None

    def __repr__(self):
        nodes = []
        cur = self.head
        while cur:
            nodes.append(str(cur.data))
            cur = cur.next
        return ' -> '.join(nodes)

    def insert(self, key, data):
        node = Node(key, data)
        if not self.head:
            self.head = node
            self.tail = node
        else:
            self.head.prev = node
            node.next = self.head
            self.head = node

    def remove(self, node):
        prev = node.prev
        prev.next = node.next

        if node == self.tail:
            self.tail = prev
        else:
            node.next.prev = prev


class LRU:
    def __init__(self, cap):
        self.hashmap = {}
        self.linkedlist = LinkedList()
        self.cap = cap

    def __repr__(self):
        return 'map: {}\tlist: {}'.format({k: v.data for k, v in self.hashmap.items()}, self.linkedlist)

    def get(self, key):
        if key in self.hashmap:
            node = self.hashmap[key]
            self.linkedlist.remove(node)
            self.linkedlist.insert(node.key, node.data)
            return node.data
        else:
            return -1

    def put(self, key, value):
        if key in self.hashmap:
            node = self.hashmap[key]
            self.linkedlist.remove(node)
        elif len(self.hashmap) == self.cap:
            tail = self.linkedlist.tail
            self.linkedlist.remove(tail)
            del self.hashmap[tail.key]

        self.linkedlist.insert(key, value)
        self.hashmap[key] = self.linkedlist.head
        print self


if __name__ == '__main__':
    cache = LRU(2)
    cache.put(1, 1)
    cache.put(2, 2)
    print cache.get(1)
    cache.put(3, 3)
    print cache.get(2)
    cache.put(4, 4)
    print cache.get(1)
    print cache.get(3)
    print cache.get(4)