first part

day3/day3.pm

@@ -0,0 +1,23 @@
+use 5.20.0;
+
+use base 'Exporter';
+
+use experimental 'signatures';
+
+our @EXPORT = qw/ path /;
+
+say path(shift) unless caller;
+
+sub path($x) {
+    my $i = 1;
+
+    return 0 if $x == 1;
+
+    $i+=2 until $x <= $i**2;
+
+    my $j = ( $x - ($i-2)**2 ) % ($i-1);
+
+    ($i-1)/2 + abs( $j - ($i-1)/2 );
+}
+
+1;

day3/day3.t

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+use Test::More;
+
+use day3;
+
+is path(12) => 3;
+is path(23) => 2;
+is path(1024) => 31;
+is path(1) => 0;
+
+done_testing;