Lithium Technologies
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Lithium Technologies Interview Question
Questions from engineers: a. Find the missing integer in a random length int[] array. b. Minimize sets of batch email addresses sent to an API, preserving address ordering, do not include duplicates in a batch. c. Define a login interface for a web app that works for a single server then multiple servers d. Develop a pub/sub interface which suppresses duplicates and supports priority levels e. Describe the architecture for a product on your resume explain how each part works in detail.
Interview Answer
Anonymous
a. lots of solutions, typical is probably Arrays.sort(), iterate through array until array[i] != (array[i+1] + 1) b. List> batches = new LinkedList>(); batches.add(new LinkedList()); outter: for (final String address : addresses) { for (final List batch : batches) { if (!batch.contains(address)) { batch.add(address); continue outter; } } List newBatch = new LinkedList(); newBatch.add(address); batches.add(newBatch); } return batches; c. Use form login or http authentication to identity a user, create a servlet session via cookie or url-rewriting. For distributed nodes, save the servlet session using a container mechanism to a backing store (rdbms or nosql). session state should have simple userid, login time, last activity time for aging logins. d. Use Java Observer/Observable to implement basic pub-sub classes, define an enum for priority and do not notify if below the current notification level. Keep notifications in a non-duplicating collection.