From d77d0d30fc323dea63d113001773910d2f0aca0b Mon Sep 17 00:00:00 2001
From: Yanick Champoux <yanick@babyl.dyndns.org>
Date: Mon, 5 Mar 2018 13:10:11 -0500
Subject: [PATCH] 2016-21

---
 2016/21/1.pl      |  39 ++++++++++++++++++
 2016/21/2.pl      |  53 ++++++++++++++++++++++++
 2016/21/input.txt | 100 ++++++++++++++++++++++++++++++++++++++++++++++
 2016/21/test      |   8 ++++
 4 files changed, 200 insertions(+)
 create mode 100644 2016/21/1.pl
 create mode 100644 2016/21/2.pl
 create mode 100644 2016/21/input.txt
 create mode 100644 2016/21/test

diff --git a/2016/21/1.pl b/2016/21/1.pl
new file mode 100644
index 0000000..6e8fa7a
--- /dev/null
+++ b/2016/21/1.pl
@@ -0,0 +1,39 @@
+use 5.20.0;
+
+use List::AllUtils qw/ first_index indexes /;
+
+my @code = split '', 'abcde'; #fgh';  # agcebfdh
+
+while( <> ) {
+    if( /swap position (\d+) with position (\d+)/ ) {
+        @code[ $1, $2 ] = @code[$2, $1];
+    }
+    elsif( /swap letter (.) with letter (.)/ ) {
+        my @x = indexes { $_ eq $1  or $_ eq $2 } @code;
+        @code[ @x ] = @code[ reverse @x ];
+    }
+    elsif( /reverse positions (\d+) through (\d+)/ ) {
+        @code[ $1..$2 ] = reverse @code[ $1..$2 ];
+    }
+    elsif( /rotate left (\d+)/ ) {
+        push @code, shift @code for 1..$1;
+    }
+    elsif( /rotate right (\d+)/ ) {
+        unshift @code, pop @code for 1..$1;
+    }
+    elsif( /move position (\d+) to position (\d+)/ ) {
+        my($x) = splice @code, $1, 1;
+        splice @code, $2, 0, $x;
+    }
+    elsif( /rotate based on position of letter (.)/ ) {
+        my $i = first_index { $_ eq $1 } @code;
+        $i++ if $i >= 4;
+        $i++;
+        unshift @code, pop @code for 1..$i;
+    }
+    else {
+        die $_;
+    }
+
+    say @code;
+}
diff --git a/2016/21/2.pl b/2016/21/2.pl
new file mode 100644
index 0000000..659ef8a
--- /dev/null
+++ b/2016/21/2.pl
@@ -0,0 +1,53 @@
+use 5.20.0;
+
+use List::AllUtils qw/ first_index indexes /;
+
+my @code = split '', 'abcdefgh'; #fgh';  # agcebfdh
+
+my @instructions = <>;
+
+use Algorithm::Combinatorics qw(permutations);
+
+my $comb = permutations(\@code);
+
+while( my $c = $comb->next ) {
+    my @code = @$c;
+    my $o = "@code";
+
+    for( @instructions ) {
+        if( /swap position (\d+) with position (\d+)/ ) {
+            @code[ $1, $2 ] = @code[$2, $1];
+        }
+        elsif( /swap letter (.) with letter (.)/ ) {
+            my @x = indexes { $_ eq $1  or $_ eq $2 } @code;
+            @code[ @x ] = @code[ reverse @x ];
+        }
+        elsif( /reverse positions (\d+) through (\d+)/ ) {
+            @code[ $1..$2 ] = reverse @code[ $1..$2 ];
+        }
+        elsif( /rotate left (\d+)/ ) {
+            push @code, shift @code for 1..$1;
+        }
+        elsif( /rotate right (\d+)/ ) {
+            unshift @code, pop @code for 1..$1;
+        }
+        elsif( /move position (\d+) to position (\d+)/ ) {
+            my($x) = splice @code, $1, 1;
+            splice @code, $2, 0, $x;
+        }
+        elsif( /rotate based on position of letter (.)/ ) {
+            my $i = first_index { $_ eq $1 } @code;
+            $i++ if $i >= 4;
+            $i++;
+            unshift @code, pop @code for 1..$i;
+        }
+        else {
+            die $_;
+        }
+    }
+
+    say "@code";
+
+    die $o if "@code" eq 'f b g d c e a h';
+
+}
diff --git a/2016/21/input.txt b/2016/21/input.txt
new file mode 100644
index 0000000..97c3f9d
--- /dev/null
+++ b/2016/21/input.txt
@@ -0,0 +1,100 @@
+move position 0 to position 3
+rotate right 0 steps
+rotate right 1 step
+move position 1 to position 5
+swap letter h with letter b
+reverse positions 1 through 3
+swap letter a with letter g
+swap letter b with letter h
+rotate based on position of letter c
+swap letter d with letter c
+rotate based on position of letter c
+swap position 6 with position 5
+rotate right 7 steps
+swap letter b with letter h
+move position 4 to position 3
+swap position 1 with position 0
+swap position 7 with position 5
+move position 7 to position 1
+swap letter c with letter a
+move position 7 to position 5
+rotate right 4 steps
+swap position 0 with position 5
+move position 3 to position 1
+swap letter c with letter h
+rotate based on position of letter d
+reverse positions 0 through 2
+rotate based on position of letter g
+move position 6 to position 7
+move position 2 to position 5
+swap position 1 with position 0
+swap letter f with letter c
+rotate right 1 step
+reverse positions 2 through 4
+rotate left 1 step
+rotate based on position of letter h
+rotate right 1 step
+rotate right 5 steps
+swap position 6 with position 3
+move position 0 to position 5
+swap letter g with letter f
+reverse positions 2 through 7
+reverse positions 4 through 6
+swap position 4 with position 1
+move position 2 to position 1
+move position 3 to position 1
+swap letter b with letter a
+rotate based on position of letter b
+reverse positions 3 through 5
+move position 0 to position 2
+rotate based on position of letter b
+reverse positions 4 through 5
+rotate based on position of letter g
+reverse positions 0 through 5
+swap letter h with letter c
+reverse positions 2 through 5
+swap position 7 with position 5
+swap letter g with letter d
+swap letter d with letter e
+move position 1 to position 2
+move position 3 to position 2
+swap letter d with letter g
+swap position 3 with position 7
+swap letter b with letter f
+rotate right 3 steps
+move position 5 to position 3
+move position 1 to position 2
+rotate based on position of letter b
+rotate based on position of letter c
+reverse positions 2 through 3
+move position 2 to position 3
+rotate right 1 step
+move position 7 to position 0
+rotate right 3 steps
+move position 6 to position 3
+rotate based on position of letter e
+swap letter c with letter b
+swap letter f with letter d
+swap position 2 with position 5
+swap letter f with letter g
+rotate based on position of letter a
+reverse positions 3 through 4
+rotate left 7 steps
+rotate left 6 steps
+swap letter g with letter b
+reverse positions 3 through 6
+rotate right 6 steps
+rotate based on position of letter c
+rotate based on position of letter b
+rotate left 1 step
+reverse positions 3 through 7
+swap letter f with letter g
+swap position 4 with position 1
+rotate based on position of letter d
+move position 0 to position 4
+swap position 7 with position 6
+rotate right 6 steps
+rotate based on position of letter e
+move position 7 to position 3
+rotate right 3 steps
+swap position 1 with position 2
diff --git a/2016/21/test b/2016/21/test
new file mode 100644
index 0000000..c6621d3
--- /dev/null
+++ b/2016/21/test
@@ -0,0 +1,8 @@
+swap position 4 with position 0
+swap letter d with letter b
+reverse positions 0 through 4
+rotate left 1
+move position 1 to position 4
+move position 3 to position 0
+rotate based on position of letter b
+rotate based on position of letter d