Week 220

2 files changed, 76 insertions, 0 deletions

diff --git a/challenge-220/cheok-yin-fung/perl/ch-1.pl b/challenge-220/cheok-yin-fung/perl/ch-1.pl
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+++ b/challenge-220/cheok-yin-fung/perl/ch-1.pl
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+# The Weekly Challenge 220
+# Task 1 Common Characters
+use v5.30.0;
+use warnings;
+use Set::Scalar;
+
+sub cc {
+    my @words = @_;
+    @words = map {lc} @words;
+    my $first_w = shift @words;
+    my $ccs = Set::Scalar->new(split "", $first_w);
+    for my $w (@words) {
+        my $cs = Set::Scalar->new(split "", $w);
+        $ccs = $ccs->intersection($cs);
+    }
+    return [sort {$a cmp $b} $ccs->elements];
+
+}
+
+use Test::More tests=>3;
+use Test::Deep;
+cmp_deeply cc("Perl", "Rust", "Raku"), ["r"];
+cmp_deeply cc("love", "live", "leave"), ["e", "l", "v"];
+use utf8;
+ok (Set::Scalar->new(cc("一石二鳥", "一二三四")->@*)->is_equal(Set::Scalar->new("一", "二")));
+
diff --git a/challenge-220/cheok-yin-fung/perl/ch-2.pl b/challenge-220/cheok-yin-fung/perl/ch-2.pl
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+# The Weekly Challenge 220
+# Task 2 Squareful
+# Brute-force approach
+use v5.30.0;
+use warnings;
+use Math::Permutation;
+use List::Util qw/all/;
+use List::MoreUtils qw/pairwise/;
+
+
+sub _fact {
+    return 1 if $_[0] == 0;
+    return $_[0] * _fact($_[0]-1);
+}
+
+sub is_perfect_sq {
+    my $a = sqrt($_);
+    return $a !~ /\./;
+}
+
+sub check_squareful {
+    my @num = @_;
+    my @num0 = @num[0..$#num-1];
+    my @num1 = @num[1..$#num];
+    my @x = pairwise {$a+$b} @num0, @num1;
+    return all {is_perfect_sq} @x;
+}
+
+sub sqf {
+    my @num = @_;
+    my %ans;
+    my $p = Math::Permutation->init(scalar @num);
+    for (1.._fact(scalar @num)) {
+        my @permuted_num = map {$num[$_-1]} $p->array;
+        $ans{join ",", @permuted_num} = 1 if check_squareful(@permuted_num);
+        $p->nxt;
+    }
+    return keys %ans;
+}
+
+say join "\n", sqf(1, 17, 8);
+say "";
+say join "\n", sqf(2, 2, 2);
+
+say join "\n", sqf(10,6,3,13,12);
+
+# Follow-up
+# Is there a distinct sequence of positive integers such that it has more than 3 squareful arrangements?
+# See also:
+# https://math.stackexchange.com/questions/1168983/arranging-numbers-from-1-to-n-such-that-the-sum-of-every-two-adjacent-number