Task 1

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diff --git a/challenge-130/cheok-yin-fung/perl/ch-1.pl b/challenge-130/cheok-yin-fung/perl/ch-1.pl
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+#!/usr/bin/perl
+# The Weekly Challenge 130
+# Task 1 Odd Number
+# Usage: $ ch-1.pl @N
+use constant BIGN => 1024;
+
+use v5.12.0;
+use warnings;
+use Test::More tests => 2;
+
+my @N = @ARGV;
+@N = (2, 5, 4, 4, 5, 5, 2) if !defined($ARGV[0]);
+
+
+say "@{oddities(@N)}";
+say the_only_odd(@N);
+
+sub the_only_odd {
+    my $s = "";
+    for my $d (@_) {
+        my $md = index((scalar reverse $s), (scalar reverse "- $d "));
+        my $pd = index((scalar reverse $s), (scalar reverse "+ $d "));
+        $md = BIGN if $md == -1 && $pd >= 0;
+        $pd = BIGN if $md == -1 && $pd == -1;
+        $s .= $md < $pd ? "+ $d " : "- $d ";
+    }
+    return eval $s;
+}
+
+
+sub oddities {
+    # return all the numbers appear odd number of times
+    # inspired by Andrezgz's Week 127 solution after reading 
+    # https://theweeklychallenge.org/blog/review-challenge-127/#PWC127TASK1
+    my @ans;
+    my %ap;
+    for (@_) {
+        $ap{$_}++ && ($ap{$_} *= -1);
+    }
+    @ans = grep {$ap{$_} > 0} keys %ap;
+    return [@ans];
+}
+
+
+ok ${oddities(1, 2, 3, 4, 3, 2, 1, 4, 4)}[0] == 4, 
+   "Example 2 using subroutine oddities";
+ok the_only_odd(1, 2, 3, 4, 3, 2, 1, 4, 4) == 4, 
+   "Example 2 using subroutine the_only_odd";