Re: OT: Finding Factor Closest To Square Root

[BrowserUk]

Update: Ignore this, it doesn't work.

You'll have tp pretend that I have M::B::F::f_w().. CPAN's being boring.

#! perl -slw
use strict;
use List::Util qw[ reduce ];

my $root = sqrt 1000;
my @pfs = ( 2, 2, 2, 5, 5, 5 );

my $near = reduce{ 
    $a * $b < $root ? $a*$b : $a
} reverse @pfs;

print +( $root - $near ) < ( $near * $pfs[0] - $root )
    ? $near
    : $near * $pfs[0];

[Roy Johnson]

I rearranged it a bit so you can just plug in your factor list and it will figure out what your number is. Note that in this case, the closest value is 5*7, but it returns 3*19.

use strict; 
use warnings;
use List::Util qw[ reduce ];

my @pfs = ( 3,5,7,19 );
my $num = reduce { $a * $b } @pfs;
my $root = sqrt $num;
print "N=$num, R=$root\n";

#the rest is the same as you had it

Here's a fix:

use strict; 
use warnings;
use List::Util qw[ reduce ];

my @pfs = ( 3,5,7,19 );
my $num = reduce { $a * $b } @pfs;
my $root = sqrt $num;
print "N=$num, R=$root\n";

my $near = reduce{ 
    abs($root - $a * $b) < abs($root - $a) ? $a*$b : $a
} reverse @pfs;

print abs($root - $near) > abs($root - ($num/$near))
    ? $num/$near
    : $near
;

[BrowserUk]

One testcase was never going to hack it. I should have thought of your method, but I was too busy trying to figure out why CPAN would install M::B::F.

[Roy Johnson]

Mine isn't perfect, either. Try 2,2,2,7,19,19, for example. I'm pretty sure the problem requires an exhaustive search of all combinations.