Solution to task 2

1 files changed, 122 insertions, 0 deletions

diff --git a/challenge-321/jo-37/perl/ch-2.pl b/challenge-321/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..b510b438e6
--- /dev/null
+++ b/challenge-321/jo-37/perl/ch-2.pl
@@ -0,0 +1,122 @@
+#!/usr/bin/perl
+
+use v5.26;
+use Test2::V0 -no_srand;
+use Test2::Tools::Subtest 'subtest_streamed';
+use Getopt::Long;
+use experimental 'signatures';
+
+use Benchmark 'cmpthese';
+
+
+### Options and Arguments
+
+my ($tests, $examples, $benchmark, $verbose);
+GetOptions(
+    'examples!' => \$examples,
+    'tests!'    => \$tests,
+    'benchmark!'    => \$benchmark,
+    'verbose!'  => \$verbose,
+) or usage();
+
+run_tests($examples, $tests, $benchmark);	# tests do not return
+
+usage() unless @ARGV == 2;
+
+sub usage {
+    die <<~EOS;
+    $0 - backspace compare
+
+    usage: $0 [-examples] [-tests] [-benchmark] [STR1 STR2]
+
+    -examples
+        run the examples from the challenge
+     
+    -tests
+        run some tests
+
+    -benchmark
+        run benchmark
+
+    STR1 STR2
+        two strings
+
+    EOS
+}
+
+
+### Input and Output
+
+say +(qw(true false))[!bs_cmp(@ARGV)];
+
+
+### Implementation
+#
+# For details see:
+# https://github.sommrey.de/the-bears-den/2025/05/18/ch-321.html#task-2
+
+sub apply_bs {
+    my @out;
+    $_ eq '#' ? pop @out : push @out, $_ for split //, shift;
+    join '', @out;
+}
+
+sub bs_cmp ($str1, $str2) {
+    apply_bs($str1) eq apply_bs($str2);
+}
+
+sub bs_cmp_subst ($str1, $str2) {
+    for ($str1, $str2) {
+        1 while s/.#//;
+    }
+    $str1 eq $str2;
+}
+
+
+### Examples and Tests
+
+sub run_tests ($examples, $tests, $benchmark) {
+    return unless $examples || $tests || $benchmark;
+
+    state sub run_example ($args, $expected, $name) {
+        my $result = bs_cmp(@$args);
+        is $result, $expected,
+            "$name: (@$args) -> " . $expected->name;
+    }
+
+    plan 3;
+
+    $examples ? subtest_streamed(examples => sub {
+        my @examples = (
+            [["ab#c", "ad#c"], T(), 'example 1'],
+            [["ab##", "a#b#"], T(), 'example 2'],
+            [["a#b", "c"], F(), 'example 3'],
+        );
+        plan scalar @examples;
+        for (@examples) {
+            run_example @$_;
+        }
+    }) : pass 'skip examples';
+
+    $tests ? subtest_streamed(tests => sub {
+        plan 4;
+        ok bs_cmp("#abc", "abc"), 'leading bs';
+        ok bs_cmp("a##", ""), 'bs moving to start';
+        ok bs_cmp("###", ""), 'multiple leading bs';
+        ok bs_cmp("abc#de###", "a"), 'delete a lot';
+    }) : pass 'skip tests';
+
+    $benchmark ? subtest_streamed(benchmark => sub {
+        plan 2;
+        my $str1 = 'a' x 1e5 . '#' x 1e5;
+        my $str2 = '';
+        ok bs_cmp($str1, $str2), 'check copy';
+        ok bs_cmp_subst($str1, $str2), 'check subst';
+        cmpthese(0, {
+                subst => sub {bs_cmp_subst($str1, $str2)},
+                copy => sub {bs_cmp($str1, $str2)},
+            });
+    }) : pass 'skip benchmark';
+
+    exit;
+}