Plug topics

Joshua Marsh joshua at
Tue Jun 11 18:25:27 MDT 2013

On Tue, Jun 11, 2013 at 12:05 PM, Sasha Pachev <sasha at> wrote:

> Part 1 - easy, you frequently see this in job interviews. Maybe not anymore
> because everybody knows it. You have a list of N unordered elements that
> contains unique numbers from 1 to N+1 with one missing. Using the amount of
> RAM that will be the same regardless of N can you find the missing number
> in one pass? Hint if you need one - remember how Gauss annoyed his math
> teacher.
> Part 2 - harder - can you do this if two numbers are missing?  Is your
> solution robust enough to avoid register overflow? Can you do it without
> resorting to BigInt arithmetic?

Is the goal of part two to accomplish all of the questions at the same
time? I can think of an easy way to find two missing, or even x missing,
but not without some form of summation which, given a sufficiently large N,
would to overflow. If the last part is solvable in one algorithm, I'd
definitely like to see a solution.

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