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.
这是leetcode上的一道题，其实这是操作系统中的一种经典的算法。
原文：http://www.cnblogs.com/qiaozhoulin/p/4841269.html