Re: recursively generating permutations

I don't know how much of an improvement this is; at least it doesn't use helper functions, for what that's worth:

sub perms {
  my $arr = shift;
  if ( !@$arr ) {
    return ( [] );
  }
  else {
    return map { my @a = @$arr;
                 my $e = splice @a, $_, 1;
                 map [ $e, @$_ ], perms( \@a ) } ( 0..$#$arr );
  }
}
[download]

Update: I changed the original to use nested maps (my original attempt to do this had a pesky bug, so I posted the working for + push version). I see that Roy Johnson had the same idea.

the lowliest monk

Comment on Re: recursively generating permutations Download Code

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Re^2: recursively generating permutations by Roy Johnson (Monsignor) on Aug 19, 2005 at 11:42 UTC
Mapifying the else block (untested): `else { return map { my @a = @$arr; my $e = splice @a, $_, 1; map [ $e, @$_ ], perms( \@a ); } 0..$#$arr; }` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]