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+#!/bin/perl
+
+=pod
+
+The Weekly Challenge - 149
+ - https://perlweeklychallenge.org/blog/perl-weekly-challenge-149/#TASK2
+
+Author: Niels 'PerlBoy' van Dijke
+
+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’.)
+
+=cut
+
+use v5.16;
+
+use bigint;
+use List::MoreUtils qw(duplicates);
+use POSIX qw(floor);
+
+sub convertBase10toBaseN($$);
+sub convertBaseNtoBase10($$);
+
+my @digits = (0 .. 9, 'A' .. 'Z');
+
+foreach my $base (2 .. 12) {
+  my $iSqrt = sqrt convertBaseNtoBase10(join('', reverse @digits[0 .. $base-1]), $base);
+
+  while ($iSqrt >= 1) {
+    my $nSqr = convertBase10toBaseN($iSqrt * $iSqrt, $base);
+
+    if (!duplicates(split//, $nSqr)) {
+      say "f($base) = $nSqr";
+      last;
+    }
+
+    $iSqrt--;
+  }
+}
+
+sub convertBase10toBaseN ($$) {
+  my ($n, $base) = @_;
+
+  state $digits = [@digits];
+
+  my @nMod; my %nMod;
+
+  while ($n) {
+    push(@nMod, $n % $base);
+    $nMod{$nMod[-1]}++;
+    $n = floor($n/$base);  # Use floor instead of int(..) for performance
+  }
+
+  return join('', reverse map {$digits->[$_]} @nMod);
+}
+
+sub convertBaseNtoBase10 ($$) {
+  my ($n, $base) = @_;
+
+  my ($res, $i) = (0, 0);
+  state $digits = { map { ($_, $i++) } (@digits) };
+
+  $i = 0;
+  foreach (reverse split //, $n) {
+    $res += $digits->{uc$_} * ($base**$i++);
+  }
+
+  return $res;
+}