use Perl

• I bet New Scientist publishes a correction (Score:1)

  by Limbic Region (3985) on 2008.06.08 17:48 (#63235) Homepage Journal

  There are a total of 24 solutions to the puzzle. These 24 solutions are comprised of 10 unique integers. If you do not consider the reverse of an integer unique, there are 5 unique integers. No matter which way you slice this - there is no way to get to "six integers" unless the spec is incomplete.

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  • Re: (Score:1)

    by depesz (7751)

    24 solutions? how did get them? can you show them?
    • Re: (Score:1)

      by Limbic Region (3985)

      Well, first the math
      
      there is 1 solution for 7, with reverse = 2
      there is 3 solutions for 9, with reverse = 6
      there is 1 solution for 11, with reverse = 2
      
      2 * 6 * 2 = 24
      
      I used a bit more complicated code than I am about to show, but you should be able to see how I came up with the 24 solutions

      for my $a (1 .. 9) {
          for my $b (grep {! /$a/} 1 .. 9) {
              for my $c (grep {! /$a|$b/ 1 .. 9) {
                  my $first = join '', $a, $b, $c;
         
      • Re: (Score:1)

        by depesz (7751)

        well, you said: 1 solution for 7, with reverse 2. actually - there are 2 solutions for 7 (4 with reverse).
        
        and your code shows them.
        
        also - you didn't take into consideration the fact that digits cannot be reused between numbers generated for various dividers.
        
        
        • Huh? (Score:1)

          by Limbic Region (3985)

          With regards to the math: What I posted about 24 solutions comprised of 10 different integers was correct (as is my code). I made a mistake when I was explaining where I came up with the 24 solutions because I didn't have the code or the results in front of me. My apologies.
          
          also - you didn't take into consideration the fact that digits cannot be reused between numbers generated for various dividers
          
          I am not sure I understand.

          for my $a (1 .. 9) { # 1 - 9
              for my $b (grep {! /$a/} 1 .. 9) { # 1
  • Re: (Score:1)

    by Smylers (2592)

    I'm sure they won't publish a correction.

    Note that the spec says to find a 3-digit number which satisfies the criteria, not the 3-digit number. That there are multiple such numbers, and you could've found a different one, doesn't violate the spec.

    Once you've done what it says, you will have 3 3-digit numbers, plus their reverses. That's 6 integers.

    Yes, other people could validly come up with a different set of 6 integers. So what? There's nothing in the spec prohibiting that! As others have noted
    • That's really too bad (Score:1)

      by Limbic Region (3985)

      I guess I won't be looking into New Scienties afterall
      
      Having worked on interesting puzzles like this as long as I can remember, as well as knowing many people who have the same interest - this is the type of puzzle no one likes to work on.
      
      A simple foot note that says: While multiple preliminary solutions are possible, the max and min will always be the same.
      
      Would have gone a long way to making others and myself happier that our solutions were correct.
      
      By the way - you have read into the spec.
      
      Once you've don
      • Re: (Score:2)

        by Ovid (2709)

        They're not usually this unclear. I think it's just a fluke, but I'd have to work through some others to be sure.