Update README for week 201

2 files changed, 72 insertions, 2 deletions

diff --git a/challenge-201/bob-lied/README b/challenge-201/bob-lied/README
index 3d4521e11d..3c3241bd85 100644
--- a/challenge-201/bob-lied/README
+++ b/challenge-201/bob-lied/README
@@ -1,4 +1,4 @@
-Solutions to weekly challenge 200 by Bob Lied
+Solutions to weekly challenge 201 by Bob Lied
 
-https://perlweeklychallenge.org/blog/perl-weekly-challenge-200/
+https://perlweeklychallenge.org/blog/perl-weekly-challenge-201/
 https://github.com/boblied/perlweeklychallenge-club/tree/master/challenge-200/bob-lied
diff --git a/challenge-201/bob-lied/perl/ch-1.pl b/challenge-201/bob-lied/perl/ch-1.pl
new file mode 100644
index 0000000000..eacbd4b736
--- /dev/null
+++ b/challenge-201/bob-lied/perl/ch-1.pl
@@ -0,0 +1,70 @@
+#!/usr/bin/env perl
+# vim:set ts=4 sw=4 sts=4 et ai wm=0 nu:
+#=============================================================================
+# ch-1.pl Perl Weekly Challenge Week 201 Task 1 Missing Numbers
+#=============================================================================
+# Copyright (c) 2023, Bob Lied
+#=============================================================================
+# You are given an array of unique numbers.
+# Write a script to find out all missing numbers in the range 0..$n
+# where $n is the array size.
+# Example 1 Input: @array = (0,1,3) Output: 2
+#   The array size i.e. total element count is 3, so the range is 0..3.
+#   The missing number is 2 in the given array.
+# Example 2 Input: @array = (0,1) Output: 2
+#   The array size is 2, therefore the range is 0..2.
+#   The missing number is 2.
+#=============================================================================
+
+use v5.36;
+
+use Getopt::Long;
+my $Verbose = 0;
+my $DoTest  = 0;
+
+GetOptions("test" => \$DoTest, "verbose" => \$Verbose);
+exit(!runTest()) if $DoTest;
+
+# Take anything that looks list-ish as arguments, squash it together
+# and remove punctuation.  What's left should be a string of numbers.
+# Split that string on white space to get a list of numbers. This
+# is too rough -- it distorts negative numbers and decimal points, but
+# good enough for the examples and some quick tests.
+my $list = "@ARGV";
+$list =~ s/[[:punct:]]/ /g;
+
+say join(' ', missingNumber( [ split(' ', $list) ] )->@* );
+
+sub missingNumber($list)
+{
+    # Make a hash where the keys are numbers 0 .. n.  Start out assuming
+    # that every number is missing.  Note that $# works on references.
+    my $n = 1 + $#{$list};
+    my %missing = map { $_ => 1 } 0 .. $n;
+
+    # The ones in the list are not missing. Numbers that are out
+    # of range would be silently ignored in delete, but just to be
+    # explicit, let's only delete things that actually exist.
+    # This convenient syntax of 0<x<n is a feature of Perl 5.32.
+    delete $missing{$_} for grep { 0 <= $_ <= $n } $list->@*;
+
+    # Sort isn't actually required.
+    return [ sort { $a <=> $b } keys %missing ];
+}
+
+sub runTest
+{
+    use Test2::V0;
+
+    is( missingNumber( [ 0,1,3   ] ), [ 2 ], "Example 1");
+    is( missingNumber( [ 0,1     ] ), [ 2 ], "Example 2");
+
+    is( missingNumber( [ 2,3     ] ), [ 0,1   ], "Missing head");
+    is( missingNumber( [ 0,1,9   ] ), [ 2,3   ], "Missing tail");
+    is( missingNumber( [ 0,5,3,1 ] ), [ 2,4   ], "Missing multiple");
+    is( missingNumber( [ 8,9     ] ), [ 0,1,2 ], "Missing whole range");
+    is( missingNumber( [ 3,-1    ] ), [ 0,1,2 ], "Missing negative");
+
+    done_testing;
+}
+