aoc2015

commit 51a829adb30dcc4dab65ffc5b2c8bc03ef68db10
parent db99c61b388768e429d1a50b4227c6d36cb1a1b8
Author: Samir Parikh <noreply@samirparikh.com>
Date:   Fri, 28 Oct 2022 21:54:35 +0000

solve day10

Diffstat:
A
day10/day10.pl
 | 
43
+++++++++++++++++++++++++++++++++++++++++++

1 file changed, 43 insertions(+), 0 deletions(-)
diff --git a/day10/day10.pl b/day10/day10.pl
@@ -0,0 +1,43 @@
+#!/usr/local/bin/perl
+# day 2015-10
+
+use strict;
+use warnings;
+use v5.32;
+
+my $string = 1113122113;
+
+#
+# solution inspired by Abigail at:
+# https://github.com/Abigail/AdventOfCode2015/blob/master/Day_10/look-and-say.pl
+#
+
+sub next_string {
+    my $string = shift;
+    my $result = "";
+
+    while ( $string =~ /\G((.)\2*)/g) {
+
+# the capture variable $1 represents what is matched in the outer most set of
+# parentheses:  (.)\2*
+# this matches for any number (.)followed by zero or more occurrences (*) of
+# itself using a back reference (\2).
+# the capture variable $2 represents the number.  The length of $1 represents
+# the number of tims that number was captured.  To see how it works, uncomment
+# the following line:
+#        say length $1, " ", $2, "s";
+# the \G anchor can be used to start the next match on the same string where the
+# last match left off.  For more information, please see:
+# https://perldoc.perl.org/perlfaq6#What-good-is-%5CG-in-a-regular-expression?
+
+        $result .= ( length $1 ) . $2;
+    }
+
+    return $result;
+}
+
+$string = next_string( $string ) foreach ( 1 .. 40 );
+say "part 1: ", length $string;
+
+$string = next_string( $string ) foreach ( 1 .. 10 ); # to reach 50 iterations
+say "part 2: ", length $string;