The function to generate all binary numbers was shown in the
solution to the Perl Weakly Challenge 049. Iterate its results and use
tr to count the occurrences of ones:
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
sub increment {
my $pos = rindex $_[0], 0;
if ($pos > -1) {
substr $_[0], $pos, 1, '1';
substr $_[0], $pos + 1, length($_[0]) - $pos - 1,
'0' x (length($_[0]) - $pos - 1);
} else {
$_[0] = '1' . ('0' x length $_[0]);
}
}
my $ones = 3;
my $length = 10;
my $n = '0' x $length;
while ($length == length $n) {
increment($n);
next unless $ones == $n =~ tr/1//;
say $n;
}
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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