Add solution for challenge 149 task 2

1 files changed, 65 insertions, 0 deletions

diff --git a/challenge-149/alexander-pankoff/perl/ch-2.pl b/challenge-149/alexander-pankoff/perl/ch-2.pl
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+++ b/challenge-149/alexander-pankoff/perl/ch-2.pl
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+#!/usr/bin/env perl
+use strict;
+use warnings;
+use feature qw'say state signatures';
+use bignum;
+no warnings qw'experimental::signatures';
+
+# TASK #2 › Largest Square
+# Submitted by: Roger Bell_West
+#
+# Given a number base, derive the largest perfect square with no repeated digits and return it as a string. (For base>10, use ‘A’..‘Z’.)
+# Example:
+#
+#     f(2)="1"
+#     f(4)="3201"
+#     f(10)="9814072356"
+#     f(12)="B8750A649321"
+
+use List::Util qw(sum0 first uniq);
+
+run() unless caller();
+
+sub run() {
+
+    my ($N) = @ARGV;
+
+    if ( !$N || $N !~ m/^\d+$/ || $N < 2 || $N > 36 ) {
+        die <<EOF;
+  Usage:
+
+    $0 N
+
+  Options:
+
+    N - a number base (between 2 and 36)
+EOF
+    }
+
+    say "f($N) = " . largest_perfet_square_without_repeated_digits_in_base($N);
+
+}
+
+sub largest_perfet_square_without_repeated_digits_in_base($base) {
+    my $x = first {
+        my $perfect_square = dec_to_base( $base, $_**2 );
+
+        my @digits = split( '', $perfect_square );
+
+        scalar uniq(@digits) == scalar @digits;
+    }
+    reverse( 0 .. int( sqrt( $base**$base - 1 ) ) );
+
+    return dec_to_base( $base, $x**2 );
+}
+
+sub dec_to_base ( $base, $n ) {
+    my @digits = ( 0 .. 9, 'A' .. 'Z' );
+
+    return $digits[$n] if $n <= $base - 1;
+
+    my $rem  = $n % $base;
+    my $next = int( $n / $base );
+
+    dec_to_base( $base, $next ) . $digits[$rem];
+}