From 464bbcb15c09813172c79820bcf526bb10cf4208 Mon Sep 17 00:00:00 2001
From: sterni <sternenseemann@systemli.org>
Date: Thu, 9 Dec 2021 16:51:02 +0100
Subject: feat(sterni/aoc/2021): day 9 solution

Change-Id: I90e7a47d5418abeff1ae7cc5757b6a8b3b0d1086
---
 users/sterni/exercises/aoc/2021/solutions.bqn | 38 +++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/users/sterni/exercises/aoc/2021/solutions.bqn b/users/sterni/exercises/aoc/2021/solutions.bqn
index d965e6047fe6..7aac53b9eaa7 100755
--- a/users/sterni/exercises/aoc/2021/solutions.bqn
+++ b/users/sterni/exercises/aoc/2021/solutions.bqn
@@ -13,6 +13,8 @@ ReadInput ← {•file.Lines ∾ •path‿"/input/day"‿(•Fmt 𝕩)}
 
 SplitOn ← ((⊢ (-1˙)⍟⊣¨ +`)∘=⊔⊢)
 
+_fix ← {𝕩 𝕊∘⊢⍟≢ 𝔽 𝕩}
+
 #
 # 2021-12-01
 #
@@ -148,3 +150,39 @@ FuelConsumption2 ← +˝∘(TriNum¨)∘|∘(-⌜)
 ! 168 = FuelConsumption2 _lowestFuelPossible day6ExampleData
 
 •Out "Day 7.2: "∾•Fmt FuelConsumption2 _lowestFuelPossible day6Input
+
+#
+# 2021-12-09
+#
+
+# part 1
+
+ParseHeightMap ← ((≠≍(≠⊑))⥊∾)∘-⟜'0'
+
+day9ExampleData ← ParseHeightMap ⟨
+  "2199943210",
+  "3987894921",
+  "9856789892",
+  "8767896789",
+  "9899965678"
+⟩
+day9Input ← ParseHeightMap ReadInput 9
+
+Rotate ← (⍉⌽)∘⊢⍟⊣ # counter clockwise
+LowPoints ← {∧´𝕩⊸(⊣<((-⊢) Rotate ∞⊸»˘∘Rotate˜))¨ ↕4}
+
+RiskLevelSum ← (+´⥊)∘(1⊸+×LowPoints)
+
+! 15 = RiskLevelSum day9ExampleData
+
+•Out "Day 9.1: "∾•Fmt RiskLevelSum day9Input
+
+# part 2
+
+NumberBasins ← ((1⊸+⊒⌾⥊)×⊢)∘LowPoints
+Basins ← {𝕩⊸((<⟜9⊣)∧(«⌈»⌈«˘⌈»˘⌈⊢)∘⊢) _fix NumberBasins 𝕩}
+LargestBasinsProduct ← {×´ 3↑ ∨ 1↓ ≠¨ ⊔⥊Basins 𝕩}
+
+! 1134 = LargestBasinsProduct day9ExampleData
+
+•Out "Day 9.2: "∾•Fmt LargestBasinsProduct day9Input
-- 
cgit 1.4.1