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+#!/usr/bin/env perl
+# vim:set ts=4 sw=4 sts=4 et ai wm=0 nu:
+#=============================================================================
+# Copyright (c) 2024, Bob Lied
+#=============================================================================
+# ch-1.pl Perl Weekly Challenge 277 Task 1 Count Common
+#=============================================================================
+# You are given two array of strings, @words1 and @words2.
+# Write a script to return the count of words that appears in both
+# arrays exactly once.
+# Example 1 Input: @words1 = ("Perl", "is", "my", "friend")
+#                  @words2 = ("Perl", "and", "Raku", "are", "friend")
+#       Output: 2
+#   The words "Perl" and "friend" appear once in each array.
+# Example 2 Input: @words1 = ("Perl", "and", "Python", "are", "very", "similar")
+#                  @words2 = ("Python", "is", "top", "in", "guest", "languages")
+#       Output: 1
+# Example 3 Input: @words1 = ("Perl", "is", "imperative", "Lisp", "is", "functional")
+#                  @words2 = ("Crystal", "is", "similar", "to", "Ruby")
+#       Output: 0
+#=============================================================================
+
+use v5.40;
+
+use Getopt::Long;
+my $Verbose = false;
+my $DoTest  = false;
+my $Benchmark = 0;
+
+GetOptions("test" => \$DoTest, "verbose" => \$Verbose, "benchmark:i" => \$Benchmark);
+exit(!runTest()) if $DoTest;
+exit( runBenchmark($Benchmark) ) if $Benchmark;
+
+my @words1 = split('', shift @ARGV);
+my @words2 = split('', shift @ARGV);
+
+say countCommon(\@words1, \@words2);
+
+sub countCommon($words1, $words2)
+{
+    use List::MoreUtils qw/frequency/;
+    my %common = frequency $words1->@*;
+
+    for ( keys %common ) { delete $common{$_} if $common{$_} != 1 }
+
+    for ( $words2->@* ) { $common{$_}++ if exists $common{$_} }
+
+    return scalar( grep { $_ == 2 } values %common);
+}
+
+sub runTest
+{
+    use Test2::V0;
+
+    is( countCommon([ qw(Perl is my friend) ],
+                    [ qw(Perl and Raku are friend) ]),         2, "Example 1");
+    is( countCommon([ qw(Perl and Python are very similar) ],
+                    [ qw(Python is top in guest languages) ]), 1, "Example 2");
+    is( countCommon([ qw(Perl is imperative Lisp is functional) ],
+                    [ qw(Crystal is similar to Ruby) ]),       0, "Example 3");
+
+    done_testing;
+}
+
+sub runBenchmark($repeat)
+{
+    use Benchmark qw/cmpthese/;
+
+    cmpthese($repeat, {
+            label => sub { },
+        });
+}
+