Merge pull request #12683 from wlmb/challenges

Solve PWC339

3 files changed, 55 insertions, 0 deletions

diff --git a/challenge-339/wlmb/blog.txt b/challenge-339/wlmb/blog.txt
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+https://wlmb.github.io/2025/09/15/PWC339/
diff --git a/challenge-339/wlmb/perl/ch-1.pl b/challenge-339/wlmb/perl/ch-1.pl
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+++ b/challenge-339/wlmb/perl/ch-1.pl
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+#!/usr/bin/env perl
+# Perl weekly challenge 339
+# Task 1:  Max Diff
+#
+# See https://wlmb.github.io/2025/09/15/PWC339/#task-1-max-diff
+use v5.36;
+use feature qw(try);
+use PDL;
+use PDL::NiceSlice;
+die <<~"FIN" unless @ARGV;
+    Usage: $0 A0 A1...
+    to find the maximum difference between products of disctinct
+    elements of the arrays A0, A1... Each array is input as a string
+    of the form "[X0 X1...]" that can be read by PDL
+    FIN
+for(@ARGV){
+    try {
+        my $in=pdl($_);
+	die "Expected four or more numbers" unless $in->dim(0)>=4;
+        my $products=$in*$in(*1);
+        my $diffs=$products-$products(*1,*1);  # Xi*Xj-Xk*Xl
+        my ($i, $j, $k, $l) = $diffs->ndcoords->mv(0,-1)->dog; #coordinates into ndarray $diffs
+        $diffs=$diffs->where(
+            ($i!=$j)&($i!=$k)&($i!=$l)
+            &($j!=$k)&($j!=$l)
+            &($k!=$l));  # select elements with no repeating coordinates
+        say "$_ -> ", $diffs->max;
+    }
+    catch($e){
+        warn $e;
+    }
+}
diff --git a/challenge-339/wlmb/perl/ch-2.pl b/challenge-339/wlmb/perl/ch-2.pl
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+#!/usr/bin/env perl
+# Perl weekly challenge 339
+# Task 2:  Peak Point
+#
+# See https://wlmb.github.io/2025/09/15/PWC339/#task-2-peak-point
+use v5.36;
+use feature qw(try);
+use PDL;
+die <<~"FIN" unless @ARGV;
+    Usage: $0 G0 G1...
+    to find the maximum value of the cumulative sums of the gains
+    in arrays G0, G1... Each argument is a string of the form "[g0 g1...]"
+    that may be understood by PDL, where gn is the gain in step n.
+    FIN
+for(@ARGV){
+    try{
+        say "$_ -> ", append(0,pdl($_))->cumusumover->max
+    }
+    catch($e){
+        warn $e;
+    }
+}