Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.
Also, creating a new cache object should take an integer for the capacity of the cache. It should either be required or default to a value.
get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(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.
cache = LRUCache.new(2)
cache.put(1, 1)
cache.put(2, 2)
cache.get(1) # returns 1
cache.put(3, 3) # evicts key 2
cache.get(2) # returns -1 (not found)
cache.put(4, 4) # evicts key 1
cache.get(1) # returns -1 (not found)
cache.get(3) # returns 3
cache.get(4) # returns 4