I got the phone interview after applying online about 2 weeks, the question is about some algorithms, there are two important questions, the first one is that there is an array which includes 99 numbers, and the numbers from 1 to 100, no same number, how could you find the missing one. The second question is that there are 8 buttons, 7 of them are some, one is a bit little heavier, and you have a balance, how could find the heavier one, you can just use the balance twice.