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花花酱 LeetCode 460. LFU Cache

Problem:

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.

Follow up:
Could you do both operations in O(1) time complexity?

Example:

Idea:
Hashtable + balanced search tree
Hashtable + double linked list
Solution 1: O(logc) c is the capacity

Solution 2: O(1)

 

花花酱 LeetCode 21: Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Solution 1: Iterative O(n)

 

Solution 2: Recursive O(n)