Check Point Software Technologies interview questions

First I had an online test in Codility - 3 medium leetcode questions in 2 hours Then I had an interview with the Team Manager in which I tell about my experience in my previous job and had a technical question to design a LRU Cache Then I had a Group Manager interview which I tell about a project and had 2 technical questions: 1. Print all the numbers from 1 to N in random order, each number one time only in O(n) 2. You have a web client which have a from in it and one of the fields is a string you know the backend server has Java running on it and it use a HashMap. How can you attack the server, then if you were the developer of the server, how would you defend this kind of attack