1 files changed, 19 insertions, 0 deletions
diff --git a/day21.bqn b/day21.bqn
new file mode 100644
index 0000000..c19e7f3
--- /dev/null
+++ b/day21.bqn
@@ -0,0 +1,19 @@
+#start ← 4‿8
+start ← 3‿10
+
+scores ← +` {𝕩+10×𝕩=0} 10| start +` (+´)⎉1 200‿2‿3 ⥊ 1+↕100
+end ← ⊑ / (»⊸<∨`) «⥊scores≥1000
+loser ←  end ⊑ ⥊scores
+roll ← 3×2+ end
+•Show loser × roll
+
+Move ← { ⟨roll,player,⟨pos,score⟩⟩:
+  pos2 ← {1+10|roll+𝕩-1}⌾(player⊸⊑) pos
+  ⟨pos2, score + pos2 × player=↕≠pos2⟩
+}
+f ← 3↓<˘⍉(↕∘≠ ≍ ⊣) ≠¨⊔+˝⍉>⥊1+↕3⥊3
+Play ← {
+ ⟨player,⟨pos,score⟩⟩: ∨´score ≥ 21 ? score ≥ 21 ;
+ ⟨player,st⟩: +´ { ⟨val,frq⟩: frq × Play (¬player)‿(Move val‿player‿st) }¨ f
+}
+•Show ⌈´ Play 0‿⟨start,⟨0,0⟩⟩