Euler#151 solution. Slow...

categories/euler/prob151-shlomif.p6

@@ -0,0 +1,37 @@
+use v6;
+
+my $total_num = 0;
+my $sum = 0;
+
+# rec is short for "recurse".
+sub rec($factor, @counts, $result)
+{
+    say @counts.join(",");
+    my $cnt = [+] @counts;
+    if $cnt == 0
+    {
+        $sum += $factor * $result;
+        $total_num += $factor;
+    }
+    else
+    {
+        for (@counts.kv) -> $size, $f
+        {
+            if $f > 0
+            {
+                my @c = @counts;
+                @c[$size]--;
+                for $size+1 .. 4 -> $s
+                {
+                    @c[$s]++;
+                }
+                rec( $factor*$f/$cnt, @c, $result + ($cnt == 1) );
+            }
+        }
+    }
+    return;
+}
+
+rec(1,[1],0);
+
+say "Result == ", ($sum / $total_num - 2).fmt("%.6f");