LRU (Least Recently Used) Cache Referring to LeetCode Q146 https://leetcode.com/problems/lru-cache/ Description LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists, otherwise return -1. void put(int key, int value) Update the value of the key if the key exists. Otherwise, add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation, evict the least recently used The functions get and put must each run in O(1) average time complexity.