Linked Lists

You are given the task to determine whether a singly linked list is a palindrome, meaning that its contents read the same backward as forward.

You're tasked with creating a function that can copy a linked list, including the random pointers, while preserving their original values and connections.

You are given two non-empty linked lists representing two non-negative integers, with their digits stored in reverse order (the ones digit first). Add the two numbers and return the sum as a linked list, also with its digits in reverse order.

Design an LRU (Least Recently Used) cache supporting get(key) and put(key, value) in O(1) average time. get returns the value or -1 if absent and marks the key as most recently used; put inserts or updates a key and, when capacity is exceeded, evicts the least recently used entry.