Done!

3 files changed, 104 insertions, 0 deletions

diff --git a/challenge-143/dave-jacoby/blog.txt b/challenge-143/dave-jacoby/blog.txt
new file mode 100644
index 0000000000..c3e15f2677
--- /dev/null
+++ b/challenge-143/dave-jacoby/blog.txt
@@ -0,0 +1 @@
+https://jacoby.github.io/2021/12/14/ninja-numbers-hiding-in-trees-the-weekly-challenge-143.html
diff --git a/challenge-143/dave-jacoby/perl/ch-1.pl b/challenge-143/dave-jacoby/perl/ch-1.pl
new file mode 100644
index 0000000000..0caded391c
--- /dev/null
+++ b/challenge-143/dave-jacoby/perl/ch-1.pl
@@ -0,0 +1,62 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say state postderef signatures };
+no warnings qw{ experimental };
+
+my @examples;
+push @examples, '( 5 * 10 )  - ( 12 * 3 )';
+push @examples, '10 + 20 - 5';
+push @examples, '(10 + 20 - 5) * 2';
+push @examples, '( ( 10 * 20 ) - 5) * 2';
+
+for my $i (@examples) {
+    my $o  = calculator($i);
+    my $o2 = bc($i);
+    say <<"END";
+    Input:  \$i = $i
+    Output: $o
+    BC:     $o2
+END
+}
+
+sub calculator( $s) {
+
+    # parens
+    while ( $s =~ /\([\s\d\+\-\*]+\)/mix ) {
+        $s =~ s/\(([\s\d\+\-\*]+\))/calculator( unbracket( $1 ))/e;
+    }
+
+    # multiplication
+
+    while ( $s =~ / \d+ \s* \* \s* \d+ /mx ) {
+        $s =~ s/( (\d+) \s* \* \s* (\d+) )/ $2 * $3 /emx;
+    }
+
+    # addition
+
+    while ( $s =~ / \d+ \s* \+ \s* \d+ /mx ) {
+        $s =~ s/( (\d+) \s* \+ \s* (\d+) )/ $2 + $3 /emx;
+    }
+
+    # subtraction
+    while ( $s =~ / \d+ \s* \- \s* \d+ /mx ) {
+        $s =~ s/( (\d+) \s* \- \s* (\d+) )/ $2 - $3 /emx;
+    }
+    return $s;
+}
+
+sub unbracket( $s ) {
+    $s =~ s/^\(//;
+    $s =~ s/\)$//;
+    return $s;
+}
+
+# This is the easy way, using pre-existing code
+sub bc( $s) {
+    my $cmd = qq{ echo '$s' | bc  };
+    my $x   = qx{$cmd};
+    chomp $x;
+    return $x;
+}
diff --git a/challenge-143/dave-jacoby/perl/ch-2.pl b/challenge-143/dave-jacoby/perl/ch-2.pl
new file mode 100644
index 0000000000..c712e2014b
--- /dev/null
+++ b/challenge-143/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,41 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say postderef signatures state };
+no warnings qw{ experimental };
+
+my @examples = qw( 6 12 24 36 );
+
+for my $i (@examples) {
+    my $o = stealthy_numbers($i);
+    say <<"END";
+    Input:  \$n = $i
+    Output: $o
+END
+}
+
+sub stealthy_numbers ( $n ) {
+    my @factors = get_factor_pairs($n);
+    for my $i ( 0 .. -1 + scalar @factors ) {
+        my ( $ix, $iy ) = $factors[$i]->@*;
+        for my $j ( $i + 1 .. -1 + scalar @factors ) {
+            my ( $jx, $jy ) = $factors[$j]->@*;
+            my $addi = $ix + $iy;
+            my $addj = $jx + $jy;
+            return 1 if abs( $addi - $addj ) == 1;
+        }
+    }
+    return 0;
+}
+
+sub get_factor_pairs( $n ) {
+    my %hash;
+    for my $x ( map { int $_ } 1 .. $n ) {
+        next unless $n % $x == 0;
+        my $y  = $n / $x;
+        my $xy = join ',', sort { $a <=> $b } $x, $y;
+        $hash{$xy} = 1;
+    }
+    return map { [ split /,/, $_ ] } sort keys %hash;
+}