I got this same polish notation question from them. It was limited to numbers and + - * / So the solution is to store the first number into a variable, then store the second number in a temp var, then perform the 3rd input (which will be an operation) on the two variables and store the answer in the first variable. and just keep looping (store in temp var, perform action on v1 and v2, store in v1) until you have no more input. Then output v1. You can ignore the second question (islands), the recruiter said that no one ever gets to it which shows that their process needs work. It's quite inconsiderate to stress out candidates in the first stage of the filter by giving them a programming challenge that no one ever gets to. I was not told about a hiring freeze. I wonder if that was position specific or if they lied to one of us.