Gambit Technologies Java Developer interview questions

I received a telephone interview just half hour after I submitted the application. The recruiter was nice and patient, he asked about my personal experience based on my resume and additional small quiz. 1. What is the difference between hashtable and hashmap? Are they synchronized? 2. Given a unsorted array of integers that values from 0 to N, with one number missing, now find out what number it is as fast as possible.