题目简述：

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.

set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

解题思路：

用一个队列存放当前的元素，用字典结构表示cache

#coding=utf-8

class LRUCache:

    # @param capacity, an integer

    def __init__(self, capacity):

        self.cap = capacity

        self.cache = {}

        self.sta = []

    # @return an integer

    def get(self, key):

        if key in self.cache:

            self.sta.remove(key)

            self.sta.append(key)

            return self.cache[key]

        else:

            return -1

    # @param key, an integer

    # @param value, an integer

    # @return nothing

    def set(self, key, value):

        if self.cap == len(self.cache) and (key not in self.cache):

            self.cache.pop(self.sta[0])

            self.sta.pop(0)

        if key in self.cache:

            self.sta.remove(key)

            self.sta.append(key)

        else:

            self.sta.append(key)

        self.cache[key] = value