I know that I'm bending the rules a little, but this does get below 50.

sub c{my$n=pop;--$n?map{my$c=$_;map$c.$_,c(@_,$n)}@_:@_}

Example:

print join " ", c qw(a b c 2);
print "\n";
print join " ", c qw(0 1 4);
print "\n";
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