Merge pull request #6277 from Util/branch-for-challenge-169

Add TWC 169 solutions by Bruce Gray : only Raku.

2 files changed, 44 insertions, 0 deletions

diff --git a/challenge-169/bruce-gray/raku/ch-1.raku b/challenge-169/bruce-gray/raku/ch-1.raku
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+++ b/challenge-169/bruce-gray/raku/ch-1.raku
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+# I often solve these kinds of tasks by implementing a is-FOO boolean function,
+# but this sequence lends itself better to generation by length-of-prime
+# when large ranges are needed. To calculate the OEIS b-file (10537 entries),
+# this method had 100x the performance of a
+# (2..Inf).grep(&some-simple-is-brilliant-function) solution,
+# where that function requires factoring-to-primes.
+#
+# However, this enormous performance difference was 
+# due to the b-file ending at the end of three-digit source primes.
+# If I compare times to compute the whole b-file plus one extra entry,
+# the perfomance falls to 4x the boolean solution.
+# I expect this pattern to recur; the more contiguous 4-brilliant numbers
+# are requested, the better the relative performance, only to have that
+# relative performance drop again as we include the first 5-brilliant number.
+
+# https://oeis.org/A078972  Brilliant numbers
+constant @brilliant_numbers = gather for 1 .. Inf -> $length {
+    my @primes = grep &is-prime, (10 ** ($length-1))
+                             ..^ (10 **  $length   );
+    .take for (@primes X* @primes).sort.squish;
+}
+
+use Test;
+is-deeply @brilliant_numbers.head(20), (4, 6, 9, 10, 14, 15, 21, 25, 35, 49, 121, 143, 169, 187, 209, 221, 247, 253, 289, 299).Seq;
+is @brilliant_numbers[10537 - 1], 994009;
+
+# The line below produces md5-exact match for https://oeis.org/A078972/b078972.txt , in less than 1 second.
+# say .key + 1, ' ', .value for @brilliant_numbers.head(10537).pairs; say '' for ^7;
diff --git a/challenge-169/bruce-gray/raku/ch-2.raku b/challenge-169/bruce-gray/raku/ch-2.raku
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+use Prime::Factor;
+
+# https://oeis.org/A052486  Achilles numbers
+constant @Achilles-numbers = (2 .. Inf).grep: {
+    my @v = .&prime-factors.Bag.values;
+
+    @v.min > 1 && ([gcd] @v) == 1;
+}
+
+
+use Test;
+plan 1;
+is-deeply @Achilles-numbers.head(20), (72, 108, 200, 288, 392, 432, 500, 648, 675, 800, 864, 968, 972, 1125, 1152,1323, 1352, 1372, 1568, 1800).Seq;
+
+# The line below produces md5-exact match for https://oeis.org/A052486/b052486.txt , in 2h7m44s :
+# say .key + 1, ' ', .value for @Achilles-numbers.head(10000).pairs;