Kaprekar numbers: Difference between revisions
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→Numeric version (medium): added '.race' for concurrency
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<pre>1 9 45 55 99 297 703 999 2223 2728 4879 4950 5050 5292 7272 7777 9999</pre>
===Numeric version (medium)===
The addition of <tt>'''race'''</tt>, in two places, allows for concurrent computation, and brings a significant speed-up in running time. <lang perl6>sub kaprekar( Int $n, Int :$base = 10 ) {
my $hi = $n ** 2;
my $lo = 0;
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print " $_" if .&kaprekar for ^10_000;
my $n;
say "\n\nBase 10 Kaprekar numbers < :10<1_000_000> = ", [+] (1 if kaprekar $_ for ^1000000);▼
(^1_000_000).race.map: { $n++ if kaprekar $_ }
say "\nBase 17 Kaprekar numbers < :17<1_000_000>";
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my &k17 = &kaprekar.assuming(:base(17));
my @results;
(^:17<1_000_000>).race.map: -> $n {
my ($h,$l) = k17 $n;
next unless $l;
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my $s17 = ($n * $n).base(17);
my $h17 = $h.base(17);
}
.say for @results.sort({$^a.chars <=> $^b.chars});</lang>
{{out}}
<pre
Base 10 Kaprekar numbers < :10<1_000_000> = 54
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24137568 GGGGGG GGGGGF000001 (GGGGGF + 000001)</pre>
Note that this algorithm allows the null string on the left, taken as zero, which automatically includes 1 as the first element of the sequence.
===Casting out nines (fast)===
<lang perl6>sub kaprekar-generator( :$base = 10 ) {
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