From 170d9a3447296a1d125315e8d7b6942d50a86c63 Mon Sep 17 00:00:00 2001
From: eutro <git@eutro.dev>
Date: Fri, 6 Dec 2024 11:16:02 +0000
Subject: [PATCH] Day 6

---
 days/day04.st | 39 ----------------------------------
 days/day06.st | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++
 days/utils.st | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 117 insertions(+), 39 deletions(-)
 create mode 100644 days/day06.st

diff --git a/days/day04.st b/days/day04.st
index 340f829..713cc46 100644
--- a/days/day04.st
+++ b/days/day04.st
@@ -1,44 +1,5 @@
-Object subclass: Posn [
-    | x y | x [^x] y [^y] x: n [x:=n] y: n [y:=n]
-    + o [ ^Posn x: x + o x y: y + o y ]
-    * n [ ^Posn x: x * n y: y * n ]
-    rotateCw [ ^Posn x: y y: x negated ]
-    rotateCcw [ ^Posn x: y negated y: x ]
-    rotate180 [ ^Posn x: x negated y: y negated ]
-
-    printOn: s [ s << '<' << x << ', ' << y << '>'. ]
-]
-Posn class extend [
-    x: x y: y [ ^Posn new x: x; y: y ]
-    up: n [ ^Posn x: 0 y: n negated ]
-    down: n [ ^Posn x: 0 y: n ]
-    left: n [ ^Posn x: n negated y: 0 ]
-    right: n [ ^Posn x: n y: 0 ]
-    up [^Posn up: 1]
-    down [^Posn down: 1]
-    left [^Posn left: 1]
-    right [^Posn right: 1]
-]
-
-Array extend [ asPosn [ ^Posn x: (self at: 1) y: (self at: 2) ] ]
 Iterable extend [
     orPats [ ^self fold: [:l :r | l or: r] ]
-    asPosns [ ^self collect: [:it | it asPosn] ]
-]
-
-Object subclass: Grid [
-    | rows | rows: n [rows:=n]
-    at: pos [ ^(rows at: pos y ifAbsent: [^nil]) at: pos x ifAbsent: [nil] ]
-    height [^rows size] width [^(rows at: 1) size]
-    allPosnsOf: elt
-    [ | oc p | oc := OrderedCollection new.
-      (1 to: self height) do:
-          [ :y | (1 to: self width) do:
-               [ :x | p := Posn x: x y: y.
-                 elt = (self at: p) ifTrue: [ oc add: p ] ] ].
-      ^oc ]
-
-    printOn: st [ rows do: [ :r | st << r; nl ] ]
 ]
 
 Object subclass: Pattern [
diff --git a/days/day06.st b/days/day06.st
new file mode 100644
index 0000000..904fd03
--- /dev/null
+++ b/days/day06.st
@@ -0,0 +1,58 @@
+Grid extend [
+    | guard dir origGuard visitedPosns |
+
+    visitedPosns: n [visitedPosns:=n]
+    visitedPosns [^visitedPosns]
+    dir [^dir]
+    guard
+    [ guard ifNotNil: [:it|^it] ifNil:
+          [ self allPosnsDo:
+                [ :pos |
+                  (self at: pos) = $^ ifTrue: [
+                      origGuard := pos.
+                      self at: pos put: $..
+                      self resetGuard.
+                      ^guard.
+                  ]]].
+      ^nil ]
+
+    resetGuard [ guard := origGuard. dir := Posn up. ]
+
+    isSolid: p [ ^(self at: p) = $# ]
+
+    copy [ ^Grid new rows: rows; restore: self state ]
+
+    stepGuard
+    [ self guard.
+      [self isSolid: (guard + dir)] whileTrue:
+          [ dir := dir rotateCcw. ].
+      guard := guard + dir. ]
+
+    state [^{self guard . self dir}]
+    restore: st [guard := st at: 1. dir := st at: 2]
+
+    guardOob [^(self at: self guard) isNil]
+
+    walkDo: block
+    [ [self guardOob] whileFalse: [block value. self stepGuard] ]
+
+    hasCycle
+    [ | fast | fast := self resetGuard copy.
+      [fast guardOob] whileFalse:
+          [self stepGuard. fast stepGuard stepGuard.
+           self state = fast state ifTrue: [^true]].
+      ^false ]
+]
+
+AOC input: [ Grid new rows: stdin toLines asArray ];
+    part1: [ :grid | | posns |
+             posns := Set new.
+             grid walkDo: [posns add: grid guard].
+             grid visitedPosns: posns.
+             posns ];
+    part2: [ :grid | | i | i := 1.
+             grid visitedPosns select:
+                 [ :p | grid at: p put: $#. i printNl. i := i + 1.
+                   [grid hasCycle] ensure: [grid at: p put: $.] ] ];
+    result: [ :grid :part | (part value: grid resetGuard) size ];
+    finish.
diff --git a/days/utils.st b/days/utils.st
index 0aa909c..b214eea 100644
--- a/days/utils.st
+++ b/days/utils.st
@@ -189,3 +189,62 @@ nil subclass: MessageChain [
     MessageChain class >> new [ ^self basicNew ]
 ]
 Object extend [ chain [ ^MessageChain new pipelineValue: self ] ]
+
+Object subclass: Posn [
+    | x y | x [^x] y [^y] x: n [x:=n] y: n [y:=n]
+    + o [ ^Posn x: x + o x y: y + o y ]
+    * n [ ^Posn x: x * n y: y * n ]
+    rotateCw [ ^Posn x: y y: x negated ]
+    rotateCcw [ ^Posn x: y negated y: x ]
+    rotate180 [ ^Posn x: x negated y: y negated ]
+
+    < o [ ^(x < o x) & (y < o y) ]
+    <= o [ ^(x <= o x) & (y <= o y) ]
+    > o [ ^(x > o x) & (y > o y) ]
+    >= o [ ^(x >= o x) & (y >= o y) ]
+    = o [ ^(x = o x) & (y = o y) ]
+    hash [ ^{x. y} hash ]
+
+    printOn: s [ s << '<' << x << ', ' << y << '>'. ]
+]
+Posn class extend [
+    x: x y: y [ ^Posn new x: x; y: y ]
+    up: n [ ^Posn x: 0 y: n negated ]
+    down: n [ ^Posn x: 0 y: n ]
+    left: n [ ^Posn x: n negated y: 0 ]
+    right: n [ ^Posn x: n y: 0 ]
+    up [^Posn up: 1]
+    down [^Posn down: 1]
+    left [^Posn left: 1]
+    right [^Posn right: 1]
+    zero [^Posn x: 0 y: 0]
+]
+
+Array extend [ asPosn [ ^Posn x: (self at: 1) y: (self at: 2) ] ]
+Iterable extend [ asPosns [ ^self collect: [:it | it asPosn] ] ]
+
+Object subclass: Grid [
+    | rows | rows: n [rows:=n]
+
+    at: pos [ ^(rows at: pos y ifAbsent: [^nil]) at: pos x ifAbsent: [nil] ]
+    at: pos put: elt
+    [ ^(rows at: pos y ifAbsent: [self error: 'Out of bounds'])
+           at: pos x put: elt ]
+
+    isInBounds: posn
+    [ posn > Posn zero ifFalse: [^false].
+      ^posn <= (Posn x: self width y: self height) ]
+
+    height [^rows size] width [^(rows at: 1) size]
+
+    allPosnsDo: block
+    [ (1 to: self height) do:
+          [ :y | (1 to: self width) do:
+               [ :x | block value: (Posn x: x y: y) ] ] ]
+    allPosnsOf: elt
+    [ | oc | oc := OrderedCollection new.
+      self allPosnsDo: [ :p | elt = (self at: p) ifTrue: [ oc add: p ] ].
+      ^oc ]
+
+    printOn: st [ rows do: [ :r | st << r; nl ] ]
+]