Here's a couple of code snippets I keep handy when I want to generate all combinations (no replacement) and permutations (all possible ways of combining a list of varying things). Enjoy.
You can probably see that I speak Perl with a lisp sometimes.
print "permute:\n";
print "[", join(", ", @$_), "]\n" for permute([1,2,3], [4,5,6], [7,8,9
+]);
print "combinations:\n";
print "[", join(", ", @$_), "]\n" for combinations(1..5);
sub permute {
my $last = pop @_;
unless (@_) {
return map [$_], @$last;
}
return map { my $left = $_; map [@$left, $_], @$last } permute(@_);
}
sub combinations {
return [] unless @_;
my $first = shift;
my @rest = combinations(@_);
return @rest, map { [$first, @$_] } @rest;
}
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