Merge pull request #7991 from jo-37/subsequent

Challenge 144

2 files changed, 89 insertions, 0 deletions

diff --git a/challenge-144/jo-37/perl/ch-1.sh b/challenge-144/jo-37/perl/ch-1.sh
new file mode 100755
index 0000000000..679a17e7de
--- /dev/null
+++ b/challenge-144/jo-37/perl/ch-1.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+perl -MMath::Prime::Util=:all -E 'forsemiprimes {say} 100'
diff --git a/challenge-144/jo-37/perl/ch-2.pl b/challenge-144/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..573885cfd3
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+++ b/challenge-144/jo-37/perl/ch-2.pl
@@ -0,0 +1,86 @@
+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0;
+use Math::Prime::Util qw(vecsum forcomb vecmin);
+use List::MoreUtils qw(singleton);
+use List::Gen qw(:iterate);
+use experimental 'signatures';
+
+our ($tests, $examples, $count);
+$count ||= 10;
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV == 2;
+usage: $0 [-examples] [-tests] [-count=C] [U1 U2]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-count=C
+    print the first C elements of the Ulam Sequence. Default: 10
+
+U1 U2
+    starting elements of an Ulam Sequence
+
+EOS
+
+
+### Input and Output
+
+gen_ulam(@ARGV)->say($count);
+
+
+### Implementation
+
+# Build a generator for an Ulam Sequence defined by the two starting
+# elements. 
+sub gen_ulam ($u1, $u2) {
+    ([$u1, $u2] + iterate {
+            # The last accessed index of the sequence is the last index
+            # of the sequence's head plus the current index in the
+            # "iterate" generator.
+            my $i = $_ + 1;
+            my @sums;
+            # Collect the sums of all pairs of already seen elements.
+            forcomb {push @sums, vecsum self()->slice(@_)} $i + 1, 2;
+            # Take the minimum unique sum larger than the last seen
+            # element.
+            vecmin grep $_ > self($i), singleton @sums;
+        })->cache->recursive;
+}
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is gen_ulam(1, 2)->take(10), [1, 2, 3, 4, 6, 8, 11, 13, 16, 18],
+        'example 1';
+
+        is gen_ulam(2, 3)->take(10), [2, 3, 5, 7, 8, 9, 13, 14, 18, 19],
+        'example 2';
+
+        is gen_ulam(2, 5)->take(10), [2, 5, 7, 9, 11, 12, 13, 15, 19, 23],
+        'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is gen_ulam(1, 2)->take(59), [1, 2, 3, 4, 6, 8, 11, 13, 16, 18,
+            26, 28, 36, 38, 47, 48, 53, 57, 62, 69, 72, 77, 82, 87, 97,
+            99, 102, 106, 114, 126, 131, 138, 145, 148, 155, 175, 177,
+            180, 182, 189, 197, 206, 209, 219, 221, 236, 238, 241, 243,
+            253, 258, 260, 273, 282, 309, 316, 319, 324, 339],
+        'https://oeis.org/A002858';
+	}
+
+    done_testing;
+    exit;
+}