Here are a couple of nested loop solutions that are probably what the *::Combinatorics modules do under the hood.
johngg@abouriou ~/perl/Monks $ perl -Mstrict -Mwarnings -E '
for my $w ( 0 .. 6 )
{
for my $x ( $w + 1 .. 7 )
{
for my $y ( $x + 1 .. 8 )
{
for my $z ( $y + 1 .. 9 )
{
say join q{}, $w, $x, $y, $z;
}
}
}
}' | wc -l
210
johngg@abouriou ~/perl/Monks $ perl -Mstrict -Mwarnings -E '
say for
map {
my $w = $_;
my $x = $w + 1;
map {
my $y = $_ + 1;
map {
my $z = $_ + 1;
map {
join q{}, $w, $x, $y, $z
} $z .. 9
} $y .. 8
} $x .. 7
} 0 .. 6;' | wc -l
210
Done just for fun, the modules are probably the best way to go.
Update: Ignore the map version as it is giving incorrect results, right number but wrong digits.
Update 2: Spotted my error in the map version, I was initialising the three inner variables too early. This works:-
johngg@abouriou ~/perl/Monks $ perl -Mstrict -Mwarnings -E '
say for
map {
my $w = $_;
map {
my $x = $_;
map {
my $y = $_;
map {
my $z = $_;
join q{}, $w, $x, $y, $z;
} ( $y + 1 ) .. 9
} ( $x + 1 ) .. 8
} ( $w + 1 ) .. 7
} 0 .. 6;' | wc -l
210
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