Re: (Golf): Sieve of Eratosthenes

[Arguile]

in reply to (Golf): Sieve of Eratosthenes

Well, looking through tilly's previous golf entries I think I'll feel fine if length($my_code) <= 3*length($tilly_code).

sub c{($k,@_)=($#_)?@_:2..($n=@_[0]);@_=map{($_%$k)?$_:0}@_;push
@_,$k;$k<=sqrt($n)?c(grep{!/^0/}@_):@_}

As for the lenght:

[arguile@cobalt ~]$ wc -L sieve_golf
    104 sieve_golf

True to the seive, it starts at k=2 eleminates n*k, then steps to next prime and repeats until k >= sqrt(n). Instead of mapping to 0 I would have loved to just drop them -- not bothering w/ the regexp for cleanup -- but I couldn't for the life of me figure out how.

The subroutine is recursive mainly b/c I had yet to try that technique and this seemed like a good time to try.

Sample output:

# display procedure blatantly stolen from Tye

2: 2
10: 2 3 5 7
50: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
100: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 
+89 97
169: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 
+89 97 101
103 107 109 113 127 131 137 139 149 151 157 163 167

Thanks to Petruchio for his rewording of ($k,@_)=($#_)?@_:2..($n=@_[0]) so I didn't produce an error. So far this seems like a great place to learn programming.</fawning>

Update

Scratched recursion and went w/ a conventional for loop, brought it down to 87 chars w/ strict compliance.

# non-strict
sub c{$n=pop;@_=2..$n;for($k=2;$k<=sqrt($n);($k)=@_){@_=grep!/^0/,(map
+{($_%$k)?$_:0}@_),$k}@_}

# strict w/ less named vars
sub c{pop;@_=2..$_;for(my$k=2;$k<=sqrt;($k)=@_){@_=grep!/^0/,(map{$_%$
+k?$_:0}@_),$k}@_}

Update

No one else was mapping, and now I see why (75 chars).

sub e{pop;@_=2..$_;for(my$k=2;$k<=sqrt;($k)=@_){@_=((grep$_%$k,@_),$k)
+;}@_}