5 files changed, 90 insertions, 0 deletions
diff --git a/challenge-205/bruce-gray/blog.txt b/challenge-205/bruce-gray/blog.txt
new file mode 100644
index 0000000000..b9b0d6392a
--- /dev/null
+++ b/challenge-205/bruce-gray/blog.txt
@@ -0,0 +1 @@
+https://blogs.perl.org/users/bruce_gray/2023/02/twc-205-exclusive-third-or-first.html
diff --git a/challenge-205/bruce-gray/perl/ch-1.pl b/challenge-205/bruce-gray/perl/ch-1.pl
new file mode 100644
index 0000000000..a6d723c0f1
--- /dev/null
+++ b/challenge-205/bruce-gray/perl/ch-1.pl
@@ -0,0 +1,16 @@
+use v5.36;
+use List::Util qw<uniq>;
+sub task1 ( $ns ) {
+    my ( $x1, $x2, $x3 ) = sort { $b <=> $a } uniq @{$ns};
+    return $x3 // $x1;
+}
+
+
+my @tests = (
+    [ [ 5, 3, 4    ], 3 ], #  5 4 3
+    [ [ 5, 6       ], 6 ], #  6 5 * Third highest is missing, so maximum is returned.
+    [ [ 5, 4, 4, 3 ], 3 ], #  5 4 3 (Aha! ties!)
+);
+use Test::More;
+plan tests => 0+@tests;
+is task1($_->[0]), $_->[1] for @tests;
diff --git a/challenge-205/bruce-gray/perl/ch-2.pl b/challenge-205/bruce-gray/perl/ch-2.pl
new file mode 100644
index 0000000000..9e2861bf96
--- /dev/null
+++ b/challenge-205/bruce-gray/perl/ch-2.pl
@@ -0,0 +1,24 @@
+use v5.36;
+use ntheory    qw<forcomb>;
+use List::Util qq<max>;
+
+# See my Raku solution for a faster algorithm.
+sub task2 ( @ns ) {
+    my $r = 0;
+
+    forcomb {
+        $r = max( $r, $ns[$_[0]] ^ $ns[$_[1]] );
+    } @ns, 2;
+
+    return $r;
+}
+
+
+my @tests = (
+    [ [  1, 2, 3,  4, 5, 6, 7 ],     7 ], #  1 xor 6 =  7
+    [ [  2, 4, 1,  3          ],     7 ], #  4 xor 3 =  7
+    [ [ 10, 5, 7, 12, 8       ],    15 ], # 10 xor 5 = 15
+);
+use Test::More;
+plan tests => 0+@tests;
+is task2(@{$_->[0]}), $_->[1] for @tests;
diff --git a/challenge-205/bruce-gray/raku/ch-1.raku b/challenge-205/bruce-gray/raku/ch-1.raku
new file mode 100644
index 0000000000..8af9db5649
--- /dev/null
+++ b/challenge-205/bruce-gray/raku/ch-1.raku
@@ -0,0 +1,13 @@
+sub task1 ( @ns ) {
+    return (.elems == 3 ?? .head !! .tail) given @ns.sort.squish.tail(3);
+}
+
+
+my @tests =
+    ( ( 5, 3, 4    ), 3 ), #  5 4 3
+    ( ( 5, 6       ), 6 ), #  6 5 * Third highest is missing, so maximum is returned.
+    ( ( 5, 4, 4, 3 ), 3 ), #  5 4 3 (Aha! ties!)
+;
+use Test;
+plan +@tests;
+is task1(.[0]), .[1] for @tests;
diff --git a/challenge-205/bruce-gray/raku/ch-2.raku b/challenge-205/bruce-gray/raku/ch-2.raku
new file mode 100644
index 0000000000..2b98b2d10c
--- /dev/null
+++ b/challenge-205/bruce-gray/raku/ch-2.raku
@@ -0,0 +1,36 @@
+# In Raku, we can solve the task in one line:
+sub task2_short { @_.unique.combinations(2).map({ [+^] .list }).max }
+
+# But with a bit of analysis, we can go *much* faster!
+# See blog post for explanation of the algorithm.
+sub task2_fast ( @ns ) {
+    sub hi-bit ( UInt $n ) { $n.log2.floor }
+
+    my %grouped = @ns.unique.classify(&hi-bit);
+
+    my ($top_group, @lesser_groups) = %grouped.sort(-*.key).map(*.value);
+
+    if !@lesser_groups {
+        my $removes_hi-bit = 1 +< hi-bit($top_group[0]);
+        return task2_fast( $top_group.list »-» $removes_hi-bit );
+    }
+    else {
+        return [max] @lesser_groups.map: {
+            ($top_group.list X+^ .list).max;
+        }
+    }
+}
+
+
+# my &task2 = &task2_short;
+my &task2 = &task2_fast;
+my @tests =
+    ( (  1, 2, 3,  4, 5, 6, 7 ),    7 ),    #  1 xor 6 =  7
+    ( (  2, 4, 1,  3          ),    7 ),    #  4 xor 3 =  7
+    ( ( 10, 5, 7, 12, 8       ),   15 ),    # 10 xor 5 = 15
+
+    ( [ flat(1 .. 4095)       ], 4095 ),    # short=113sec, fast=5sec !!!
+;
+use Test;
+plan +@tests;
+is task2(.[0]), .[1] for @tests;