Re: the hourglass problem

From	root <NoEMail@home.org>
Newsgroups	sci.logic, rec.puzzles, sci.math.num-analysis, comp.programming
Subject	Re: the hourglass problem
Date	2012-01-01 05:51 +0000
Organization	Linux Advocacy
Message-ID	<jdos8s$ov8$1@dont-email.me> (permalink)
References	<7f48dfe5-ca54-49ca-8cb9-5ae686e96f92@c42g2000prb.googlegroups.com>

Cross-posted to 4 groups.

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RichD <r_delaney2001@yahoo.com> wrote:
> You're given a 7 minute, and a 4 minute, sand
> hourglass.  Measure a 9 minute interval, in the first
> 9 minutes.  (no 'setup' period)
> 
> ok, this is trivial.  But as computer nerds, we're
> interested in general solutions.  So, given hourglasses
> of n and m minutes:
> 
> 1)  Can you devise a formula which generates a list of
>   all possible intervals produced by them?
> 
> 2)  And an algorithm, which generates the interval,
>   for any given number on the list.
> 
> Of course, this is solvable via brute force, but we
> want something efficient.
> 
> PS  The problem stated above is a Google
> interview question!  Which lowers my estimate of
> their intellectual prowess.
> 
> --
> Rich

This problem is very interesting. After you realize
how to get 9 minutes, you then realize you are
able to get 4 minutes, 7 minutes, and then every
integer minute thereafter. So the numbers realizable
without delay are:
4,7,8,9,10,11,12........

Then, clearly, with a 7 minute delay you can generate
every integer minute.

Thread

the hourglass problem RichD <r_delaney2001@yahoo.com> - 2011-12-31 18:03 -0800
  Re: the hourglass problem William Elliot <marsh@rdrop.com> - 2011-12-31 19:21 -0800
    Re: the hourglass problem Dave Dodson <dave_and_darla@Juno.com> - 2011-12-31 19:41 -0800
      Re: the hourglass problem William Elliot <marsh@rdrop.com> - 2012-01-01 19:48 -0800
        Re: the hourglass problem Patricia Shanahan <pats@acm.org> - 2012-01-01 20:44 -0800
          Re: the hourglass problem William Elliot <marsh@rdrop.com> - 2012-01-01 23:08 -0800
            Re: the hourglass problem Patricia Shanahan <pats@acm.org> - 2012-01-02 07:55 -0800
              Re: the hourglass problem Dr Nick <3-nospam@temporary-address.org.uk> - 2012-01-02 16:17 +0000
                Re: the hourglass problem Robert Wessel <robertwessel2@yahoo.com> - 2012-01-03 03:37 -0600
    Re: the hourglass problem Remysun <remysun2000@yahoo.com> - 2012-01-02 17:10 -0800
      Re: the hourglass problem "BartC" <bc@freeuk.com> - 2012-01-03 01:12 +0000
  Re: the hourglass problem root <NoEMail@home.org> - 2012-01-01 05:51 +0000
    Re: the hourglass problem William Elliot <marsh@rdrop.com> - 2012-01-01 20:04 -0800
      Re: the hourglass problem Duncan Booth <duncan.booth@invalid.invalid> - 2012-01-02 11:42 +0000
    Re: the hourglass problem RichD <r_delaney2001@yahoo.com> - 2012-01-03 15:05 -0800
      Re: the hourglass problem Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-03 15:19 -0800
        Re: the hourglass problem PT <ptanenbaum@consultant.com> - 2012-01-04 12:28 -0800
          Re: the hourglass problem Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-04 13:44 -0800
        Re: the hourglass problem Dave Dodson <dave_and_darla@Juno.com> - 2012-01-04 22:55 -0800
          Re: the hourglass problem Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-04 23:55 -0800
            Re: the hourglass problem "Harry Vaderchi" <admin@127.0.0.1> - 2012-01-05 10:06 +0000
              Re: the hourglass problem "BartC" <bc@freeuk.com> - 2012-01-05 13:44 +0000
                Re: the hourglass problem Patricia Shanahan <pats@acm.org> - 2012-01-05 08:13 -0800
                Re: the hourglass problem Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-05 11:55 -0800
                Re: the hourglass problem JohnF <john@please.see.sig.for.email.com> - 2012-01-06 04:40 +0000
            Re: the hourglass problem Dave <dave_and_darla@Juno.com> - 2012-01-05 15:37 -0800
              Re: the hourglass problem Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-05 16:02 -0800
  Re: the hourglass problem Duncan Booth <duncan.booth@invalid.invalid> - 2012-01-02 11:50 +0000
  Re: the hourglass problem Frederick Williams <freddywilliams@btinternet.com> - 2012-01-02 17:18 +0000
    Re: the hourglass problem msb@vex.net (Mark Brader) - 2012-01-02 17:40 -0600
      Re: the hourglass problem RichD <r_delaney2001@yahoo.com> - 2012-01-02 17:37 -0800
        Re: the hourglass problem msb@vex.net (Mark Brader) - 2012-01-02 23:45 -0600
        Re: the hourglass problem "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-01-03 10:06 +0100
        Re: the hourglass problem Thomas Mlynarczyk <thomas@mlynarczyk-webdesign.de> - 2012-01-03 12:51 +0100
          Re: the hourglass problem Nicolas Neuss <lastname@scipolis.de> - 2012-01-03 18:07 +0100
            Re: the hourglass problem Thomas Mlynarczyk <thomas@mlynarczyk-webdesign.de> - 2012-01-03 21:58 +0100
        Re: the hourglass problem Frederick Williams <freddywilliams@btinternet.com> - 2012-01-03 13:22 +0000
      Re: the hourglass problem "BartC" <bc@freeuk.com> - 2012-01-03 12:59 +0000
    Re: the hourglass problem Thomas Mlynarczyk <thomas@mlynarczyk-webdesign.de> - 2012-01-03 12:47 +0100
  Re: the hourglass problem Frederick Williams <freddywilliams@btinternet.com> - 2012-01-05 14:09 +0000
    Re: the hourglass problem Patricia Shanahan <pats@acm.org> - 2012-01-05 08:17 -0800
      Re: the hourglass problem Frederick Williams <freddywilliams@btinternet.com> - 2012-01-05 16:27 +0000
      Re: the hourglass problem Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-05 11:57 -0800
      Re: the hourglass problem JohnF <john@please.see.sig.for.email.com> - 2012-01-06 06:42 +0000

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