This is an inelegant brute force approach:

my $num1 = 150;
my $num2 = 1000;

# set which is biggest and which smallest
my $max = ($num1 > $num2)? $num1 : $num2;
my $min = ($num1 < $num2)? $num1 : $num2;

for $divisor (reverse 0 .. $min) {
    # fail unless our divisor divides evenly into $min
    next if $min % $divisor;
    # fail unless our divisor divides evenly into $max
    next if $max % $divisor;
    print "Largest common divisor is $divisor\n";
  last;
}
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This is O(n) in that the bigger the smaller number the longer this will take to run. For a more elegant approach use Euclid's recursive algorithm as suggested by larsen it is O(log $a * log $b) - ie so much more efficient it is not funny!:

print euclid(15000,1260);

sub euclid {
   my( $a, $b ) = @_;
 return ($b) ? euclid( $b, $a % $b ) : $a;
}
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cheers

tachyon

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