From: "David A. Black" <dblack@...>
Date: 2008-07-20T03:36:39+09:00
Subject: Re: The next number that is not in an array

Hi --

On Sun, 20 Jul 2008, Bill Walton wrote:

> Hi All,
>
> David A. Black wrote:
>> On Thu, 17 Jul 2008, Tim Conner wrote:
>>
>>> I want to increment the current value of a variable to
>>> the next number that does not appear in an array of
>>> restricted numbers.
>>> e.g.
>>> restricted_numbers = [2,3,4,5,8,10,15,29]
>>>
>>> if the variable is currently storing 11 then I want
>>> to increment it to 12, however if the variable is
>>> currently storing 1 then I want to increment it to 6.
>>>
>>> How is this done in ruby?
>>
>> Here's a pretty terse way -- maybe too terse, and rather
>> side-effect-ish, but kind of interesting:
>>
>>    true while restricted_numbers.include?(n+=1)
>
> I've been working in Rails for about 3 years now, but have only recently
> begun to really dig in to Ruby.  I say that in hopes you'll answer a couple
> of questions to help me 'dig' in more productive locations :-)
>
> My first take on this 'quiz' was to initialize a new array with members
> between the current value and the largest restricted number (including the
> largest), subtract the restricted_number array from the new one, and return
> the first member of the result.  None of the solutions proposed involved
> anything like this, so I'm hoping one or more of you will say a little bit
> about why.

So like this?

irb(main):020:0> a = [2,3,4,8,12,13,15]
=> [2, 3, 4, 8, 12, 13, 15]
irb(main):021:0> ([*a[0]..20] - a).shift
=> 5

It's a cool idea, though I would find it somewhat hard to see what's
going on at a glance than some of the others.

> Second question has to do with comments Robert Dober made like '10 times
> slower' and '50 times faster'.  I'm assuming there's some benchmarking
> capability I need to learn more about.  Could somebody point me?  Also, is
> this capability available in IRB?

Have you used the Benchmark module? It's the usual tool for getting
comparisons of different snippets that do the same thing as each
other.


David

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