Missing number(s) Interview Question Redux

Question

The common interview problem of determining the missing value in a range from 1 to N has been done a thousand times over. Variations include 2 missing values up to K missing val

Answer 1

Because the numbers are taken from a small, finite range, they can be 'sorted' in linear time.

All we do is initialize an array of 100 booleans, and for each input, set the boolean corresponding to each number in the input, and then step through reporting the unset booleans.