You are given an array of strings tokens that represents an arithmetic expression in Reverse Polish Notation (RPN). Your task is to evaluate the expression and return the result as an integer.
Design and implement a queue using only two stacks. The queue should support the basic operations of a normal queue: enqueue, dequeue, peek, and checking if the queue is empty.
Given a string ’s’, remove duplicate letters so that every letter appears once and only once. The result should be the smallest lexicographical order among all possible results.
You are given a nested list of integers nestedList, where each element can either be an integer or a sublist containing integers or other sublists. Implement an iterator to flatten this nested list.
