Solution to task 2

1 files changed, 108 insertions, 0 deletions

diff --git a/challenge-338/jo-37/perl/ch-2.pl b/challenge-338/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..1861f7c460
--- /dev/null
+++ b/challenge-338/jo-37/perl/ch-2.pl
@@ -0,0 +1,108 @@
+#!/usr/bin/perl
+
+use v5.26;
+use Test2::V0 qw(!float -no_srand);
+use Test2::Tools::Subtest 'subtest_streamed';
+use Getopt::Long;
+use experimental 'signatures';
+
+use PDL;
+use PDL::NiceSlice;
+
+### Options and Arguments
+
+my ($tests, $examples, $verbose);
+GetOptions(
+    'examples!' => \$examples,
+    'tests!'    => \$tests,
+    'verbose!'  => \$verbose,
+) or usage();
+
+run_tests($examples, $tests);	# tests do not return
+
+usage() unless @ARGV;
+
+sub usage {
+    die <<~EOS;
+    $0 - max distance
+
+    usage: $0 [-examples] [-tests] [-verbose] [--] [L...]
+
+    -examples
+        run the examples from the challenge
+     
+    -tests
+        run some tests
+
+    L...
+        list of integer lists in a form like 'a,b,c;d,e' or '[a b c] [d e]'
+
+    EOS
+}
+
+
+### Input and Output
+
+say max_distance(@ARGV);
+
+
+### Implementation
+#
+# For details see:
+# https://github.sommrey.de/the-bears-den/2025/09/12/ch-338.html#task-2
+
+sub max_distance {
+    state $diff = long -1, 1;
+    state $sel = indx [0, 1, 0], [0, 0, 1];
+    $PDL::undefval = badvalue long;
+    (my $m = long @_)->badflag(1);
+    my $mm = cat +($m->minmaximum)[0, 1];
+    my $mm2 = maximum_n_ind $mm * $diff(*1), 2;
+    my $cand = $mm2->cat($mm->index1d($mm2))
+        ->index1d($sel)->xchg(0, 1)->inner($diff);
+
+    $cand(,1)->where($cand(,0))->max;
+}
+
+
+### Examples and Tests
+
+sub run_tests ($examples, $tests) {
+    return unless $examples || $tests;
+
+    state sub run_example ($args, $expected, $name) {
+        my $result = max_distance(@$args);
+        is $result, $expected,
+            "$name: (@{[map qq([@$_]), @$args]}) -> $expected";
+    }
+
+    plan 2;
+
+    $examples ? subtest_streamed(examples => sub {
+        my @examples = (
+            [[[4, 5, 7], [9, 1, 3, 4]], 6, 'example 1'],
+            [[[2, 3, 5, 4], [3, 2, 5, 5, 8, 7]], 6, 'example 2'],
+            [[[2, 1, 11, 3], [2, 5, 10, 2]], 9, 'example 3'],
+            [[[1, 2, 3], [3, 2, 1]], 2, 'example 4'],
+            [[[1, 0, 2, 3], [5, 0]], 5, 'example 5'],
+        );
+        plan scalar @examples;
+        for (@examples) {
+            run_example @$_;
+        }
+    }) : pass 'skip examples';
+
+    $tests ? subtest_streamed(tests => sub {
+        my @tests = (
+            [[[2, 5, 10], [5, 6, 7], [1, 4, 9]], 9, 'max_1/min_1'],
+            [[[1, 5, 10], [5, 6, 7], [2, 4, 7]], 8, 'max_1/min_2'],
+            [[[1, 5, 10], [5, 6, 7], [3, 4, 9]], 8, 'max_2/min_1'],
+        );
+        plan scalar @tests;
+        for (@tests) {
+            run_example @$_;
+        }
+    }) : pass 'skip tests';
+
+    exit;
+}