in reply to magic squares

sflitman,
I finally have a solution I am happy with. It only loops 206 times as that's how many possible 3x3 magic squares using 1-26 there are. Of course, I spent far more of my time (not to mention tilly and tye) figuring out how to get this solution then it would have taken just to let a naive brute force run. Enjoy. This should scale something close to O(N) where N is the number of names that you want to check.
#!/usr/bin/perl use strict; use warnings; my @possible; for my $x (5 .. 22) { for my $y (grep {$_ != $x} 1 .. int((25 - $x) / 2)) { my $max = 26 - $x - 2 * $y; my $min = $x - 2 * $y - 1; for my $z (grep {$_ != $x && $_ != $y} 1 .. ($min < $max ? $mi +n : $max)) { my @square = ( ($x + $y), ($x + $z), ($x - $y - $z), ($x - 2 * $y - $z), ($x), ($x + 2 * $y + $z), ($x + $y + $z), ($x - $z), ($x - $y) ); push @possible, join '', map chr($_ + 64), @square; } } } NAME: for (qw/PAUL JOHN MARTY SHEILA SMACK SUZY ELSA/) { for my $square (@possible) { my $name = $_; $name =~ s/[$square]//g; if (! length($name)) { print "$_ is contained within $square\n"; next NAME; } } print "No solution for $_\n"; }

Cheers - L~R

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Re^2: magic squares
by tilly (Archbishop) on Apr 10, 2009 at 01:20 UTC
    Nit. There are actually 1648 magic squares. Rotation and reflection can generate the rest from the 206 that you are producing.