TWC290

Challenge Link

Task1

We check if the double of a key also exists in the hash:

#!/usr/bin/env perl
use strict;
use warnings;

sub double_exist{
  my %h;
  $h{$_}++ foreach @{$_[0]};
  map{return 1 if exists $h{$_ * 2}} keys %h;
  0
}

printf "%d\n",double_exist([6,2,3,3]);
printf "%d\n",double_exist([3,1,4,13]);
printf "%d\n",double_exist([2,1,4,2]);

Task2

After removing the spaces and using the last digit as the payload, then if the digit is less than 9, we add it to the sum, otherwise we clamp its double to be less than or equal to 9 and add it to the sum. Finally, we check if the sum of the accumulated result and the payload is divisible by 10:

#!/usr/bin/env perl
use strict;
use warnings;

sub luhns_algorithm{
  my ($str) = @_;
  $str =~ tr/0-9//dc;
  my $p = chop $str;
  my ($sum,$even) = (0) x 2;
  foreach my $d(reverse split '',$str){
    $sum += $even ? $d : 2 * $d > 9 ? 2 * $d - 9 : 2 * $d;
    $even = !$even
  }
  ($sum + $p) % 10 == 0
}

printf "%d\n",luhns_algorithm('17893729974');
printf "%d\n",luhns_algorithm('4137 8947 1175 5904');
printf "%d\n",luhns_algorithm('4137 8974 1175 5904');