Day 10

days/day10.st

@@ -0,0 +1,56 @@
+Object subclass: TrailMap [
+    | heightMap scores allDirs |
+    scores [^scores]
+
+    initFor: pos [ ^Set new add: pos; yourself ]
+    initScore [ ^Set new ]
+    combineScore: score with: other [ score addAll: other. ^score ]
+    numberFromScore: score [ ^score size ]
+
+    initialize [ allDirs := {Posn up. Posn down. Posn left. Posn right}. ]
+    heights: hm [ heightMap := hm. self initScores. ]
+    initScores
+    [ | rows |
+      rows := (1 to: heightMap height) collect: [
+          :y | (1 to: heightMap width) collect: [
+              :x | | pos | pos := Posn x: x y: y.
+              ((heightMap at: pos) = 9)
+                  ifTrue: [self initFor: pos]
+                  ifFalse: [nil]]].
+      scores := Grid new rows: rows ]
+
+    computeScores
+    [ (8 to: 0 by: -1) do: [:i | self computeScoresForHeight: i]. ]
+
+    computeScoresForHeight: h
+    [ | h1 | h1 := h + 1.
+      heightMap allPosnsDo: [
+          :pos |
+          (heightMap at: pos) = h ifTrue: [
+              | res | res := self initScore.
+              allDirs collect: [
+                  :off | | offp | offp := pos + off.
+                  ((heightMap at: offp) = h1) ifTrue:
+                      [ res := self combineScore: res with: (scores at: offp) ]].
+              scores at: pos put: res ]]]
+
+    trailheadScores
+    [ ^(heightMap allPosnsOf: 0) collect: [:p | self numberFromScore: (scores at: p)] ]
+]
+
+TrailMap subclass: TrailMapP2 [
+    initFor: pos [^1]
+    initScore [^0]
+    combineScore: score with: other [^score + other]
+    numberFromScore: score [^score]
+]
+
+AOC input: [ | rows |
+             rows := stdin toLines asArray collect: [
+                 :line | line asArray collect: [:it | it digitValue]].
+             Grid new rows: rows ];
+    part1: TrailMap; part2: TrailMapP2;
+    result: [ :heights :Class | | map |
+              map := Class new heights: heights.
+              map computeScores trailheadScores sum ];
+    finish.