From 82b83c029f8b4f262d421deff04dc1b3ee00d4ce Mon Sep 17 00:00:00 2001
From: Panadestein <rpana92@gmail.com>
Date: Tue, 17 Dec 2024 01:00:38 +0100
Subject: [PATCH] feat: learn from dzaima's solution of day 16.

---
 src/aoc24.org     | 20 ++++++++++++++++++++
 src/bqn/aoc24.bqn | 10 ++++++++++
 2 files changed, 30 insertions(+)

diff --git a/src/aoc24.org b/src/aoc24.org
index cd10d54..97f0801 100644
--- a/src/aoc24.org
+++ b/src/aoc24.org
@@ -338,6 +338,26 @@ powers of the adjacency matrix. This method is unfortunately slower than simple
 #+RESULTS:
 : "Computed 1446158 and 1446175 in 0.0177348094s"
 
+** XVI
+
+I dislike graph algorithms for their messy, imperative solutions with impurities and fancy data structures.
+This problem is usually solved with Dijkstra, but after days of "Fortranized" DFS and BFS, I turned to an
+expert array programmer's [[https://github.com/dzaima/aoc][solution]] and reworked mine:
+
+#+begin_src bqn :tangle ./bqn/aoc24.bqn :exports both
+  XVI ← {
+    r‿s‿e ← ⟨'#'⊸≠, 'S'⊸=, 'E'⊸=⟩{𝕎𝕩}¨<inp ← >•FLines Input𝕩
+    _fp ← {𝔽∘⊢⍟≢⟜𝔽_𝕣∘⊢⍟≢⟜𝔽𝕩} ⋄ _m ← {𝕩{𝕏𝕨}¨𝔽⟨»,»˘,«,«˘⟩} ⋄ inf ← -2⋆31
+    dij ← ⌊´∘{⟨⊢_m, 1⊸⌽⌊1⊸⌽⁼, ⊢⟩{r<⊸×𝕎𝕩}¨⟨𝕩+1, 𝕩+1e3, 𝕩⟩}_fp 0‿inf‿0‿0×<s
+    mn‿mr‿mrc ← r⊸∧¨¨ {⟨¯1+2⊸⌽_m𝕩, 1⌽𝕩-1e3, 1⌽⁼𝕩-1e3⟩=<𝕩}dij
+    eins ⇐ inf -˜ opt ← (⌊´dij) ⊑˜⊑/○⥊⟜(↕≢)e
+    zwei ⇐ +´⥊∨´ {∨´⟨mn∧2⊸⌽𝕩, mr∧1⌽𝕩, mrc∧1⌽⁼𝕩, 𝕩⟩}_fp e<⊸∧dij=opt
+  }
+  XVI _is 16
+#+end_src
+
+#+RESULTS:
+: "Computed 99448 and 1 in 0.049628195s"
 
 #+BEGIN_EXPORT html
   <div style="text-align: center; font-size: 2em; padding: 20px 0;">
diff --git a/src/bqn/aoc24.bqn b/src/bqn/aoc24.bqn
index 1f09e4d..c8a5dc6 100644
--- a/src/bqn/aoc24.bqn
+++ b/src/bqn/aoc24.bqn
@@ -175,3 +175,13 @@ XV ← {
   w↩wd ⋄ rid DFS´m ⋄ zwei ⇐ +´⥊100‿1×⎉1>/○⥊⟜(↕≢)'['=w
 }
 XV _is 15
+
+XVI ← {
+  r‿s‿e ← ⟨'#'⊸≠, 'S'⊸=, 'E'⊸=⟩{𝕎𝕩}¨<inp ← >•FLines Input𝕩
+  _fp ← {𝔽∘⊢⍟≢⟜𝔽_𝕣∘⊢⍟≢⟜𝔽𝕩} ⋄ _m ← {𝕩{𝕏𝕨}¨𝔽⟨»,»˘,«,«˘⟩} ⋄ inf ← -2⋆31
+  dij ← ⌊´∘{⟨⊢_m, 1⊸⌽⌊1⊸⌽⁼, ⊢⟩{r<⊸×𝕎𝕩}¨⟨𝕩+1, 𝕩+1e3, 𝕩⟩}_fp 0‿inf‿0‿0×<s
+  mn‿mr‿mrc ← r⊸∧¨¨ {⟨¯1+2⊸⌽_m𝕩, 1⌽𝕩-1e3, 1⌽⁼𝕩-1e3⟩=<𝕩}dij
+  eins ⇐ inf -˜ opt ← (⌊´dij) ⊑˜⊑/○⥊⟜(↕≢)e
+  zwei ⇐ +´⥊∨´ {∨´⟨mn∧2⊸⌽𝕩, mr∧1⌽𝕩, mrc∧1⌽⁼𝕩, 𝕩⟩}_fp e<⊸∧dij=opt
+}
+XVI _is 16