Update ch-1.pl

Shift the Van Eck sequence to prepare $a_{n+1}$ knowing $a_n$.

1 files changed, 20 insertions, 0 deletions

diff --git a/challenge-014/jaime/perl5/ch-1.pl b/challenge-014/jaime/perl5/ch-1.pl
index 220183b345..18041efa05 100644
--- a/challenge-014/jaime/perl5/ch-1.pl
+++ b/challenge-014/jaime/perl5/ch-1.pl
@@ -4,3 +4,23 @@
 # 
 # Write a script to generate Van Eck’s sequence.
 
+my @ecks = (0);
+print "0\n"; # start the sequence.
+
+for (my $n = 0; ; $n++) {
+    $a1 = 0;
+    $an = shift @ecks;
+
+    my $m = 1; # the distance between matching entries.
+    for my $am (@ecks) {
+	if ($an == $am) {
+	    $a1 = $m;
+	    last; # only update with most recent entry.
+	}
+    } continue { $m++; }
+
+    unshift @ecks, $an;
+    unshift @ecks, $a1; # series is stored in reverse.
+
+    print "@ecks[0]\n"; # filter series with `perl ch-1.pl | head -n $LENGTH`
+}