Design and implement a data structure for Least
Frequently Used (LFU) cache. It should support the following operations:
get and put.
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 reaches its capacity, it should invalidate the least frequently used item
before inserting a new item. For the purpose of this problem, when there is a tie (i.e., two
or more keys that have the same frequency), the least recently used key would be
evicted.
Note that the number of times an item is used is the number of calls to
the get and put functions for that item since
it was inserted. This number is set to zero when the item is removed.
Follow up:
Could you do both operations in O(1) time complexity?
Example:
LFUCache cache = new LFUCache( 2 /* capacity */ ); 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.get(3); // returns 3. cache.put(4, 4); // evicts key 1. cache.get(1); // returns -1 (not found) cache.get(3); // returns 3 cache.get(4); // returns 4