Beefy Boxes and Bandwidth Generously Provided by pair Networks
There's more than one way to do things
 
PerlMonks  

Re: Challenge: Another Infinite Lazy List

by kvale (Monsignor)
on Mar 17, 2005 at 21:20 UTC ( #440547=note: print w/ replies, xml ) Need Help??


in reply to Challenge: Another Infinite Lazy List

Here is a simple iterative solution:

my @factors = (2,3,5); # Assmue increasing sequence my $seq_len = 10; my $index = 0; foreach my $num (1..$seq_len*$factors[0]) { foreach my $factor (@factors) { unless ($num % $factor) { print "$num "; $index++; last; } } last if $index >= $seq_len; }

-Mark


Comment on Re: Challenge: Another Infinite Lazy List
Download Code
Re^2: Challenge: Another Infinite Lazy List
by tall_man (Parson) on Mar 18, 2005 at 01:13 UTC
    If you want a pure iterative solution, you could compute a factor wheel and print everything but the usual trial divisors. The code looks messier, but it requires no mod calculations in the loop, just adds. I computed the wheel using Math::Big::Factors (so for people following the original articles, we have come full circle...).

      I am confused. Where is the "infinite lazy list"?

      In the implementation I posted, a variable like

      my $lazy235 = challenge( 2, 3, 5 );
      is, effectively, an infinite lazy list. One can repeatedly extract an arbitrarily long prefix from it, using take, or repeatedly find its n-th element with something like:
      sub nth { my $ll = shift; my $n = shift; die "Invalid argument: $n\n" if $n < 0; return $n == 0 ? head( $ll ) : nth( tail( $ll ), $n - 1 ); }
      For example, the following:
      my @first_50 = take( 50, $lazy235 ); my @again = take( 50, $lazy235 ); print "@first_50\n\n@again\n\n"; for ( map int( rand( 1000 ) ), ( 1 .. 5 ) ) { printf "%3d %d\n", $_, nth( $lazy235, $_ ); }
      prints out something like
      0 2 3 4 5 6 8 9 10 12 14 15 16 18 20 21 22 24 25 26 27 28 30 32 33 34 +35 36 38 39 40 42 44 45 46 48 50 51 52 54 55 56 57 58 60 62 63 64 65 +66 0 2 3 4 5 6 8 9 10 12 14 15 16 18 20 21 22 24 25 26 27 28 30 32 33 34 +35 36 38 39 40 42 44 45 46 48 50 51 52 54 55 56 57 58 60 62 63 64 65 +66 347 474 857 1168 530 723 994 1355 579 789

      the lowliest monk

        My reply was not meant to be an "infinite lazy list". It was a reply to another poster who had an interative solution, giving another way to do it. I perfer the lazy list solutions myself.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://440547]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others taking refuge in the Monastery: (15)
As of 2014-12-18 22:00 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    Is guessing a good strategy for surviving in the IT business?





    Results (66 votes), past polls