From 6b558d93306823c7235cef56065f566ad897e800 Mon Sep 17 00:00:00 2001
From: eutro <git@eutro.dev>
Date: Sat, 7 Dec 2024 11:38:55 +0000
Subject: [PATCH] Day 7 cleanup

---
 days/day07.st | 25 +++++++++++++++----------
 days/utils.st | 27 +++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/days/day07.st b/days/day07.st
index 26d92b9..3a492a0 100644
--- a/days/day07.st
+++ b/days/day07.st
@@ -6,7 +6,9 @@ Object subclass: MulOp
     ^tgt quo: n ] ]
 MulOp subclass: CatOp
 [ tryDo: n target: tgt
-  [ | p10 | p10 := 10 raisedTo: ((n + 1) log: 10) ceiling.
+  [ | p10 |
+    p10 := (n + 1) ceilingLog: 10.
+    p10 := 10 raisedTo: p10.
     ^super tryDo: p10 target: tgt - n ] ]
 
 Object subclass: Equation [
@@ -17,24 +19,27 @@ Object subclass: Equation [
 
     printOn: dst [dst << target << ': ' << numbers]
 
+    "Backtracking search right-to-left over the number sequence."
     canSolveFrom: idx target: tgt with: ops
-    [ | n | n := numbers at: idx.
+    [ | n n1 ok | n := numbers at: idx.
       idx = 1 ifTrue: [^n = tgt].
       tgt < n ifTrue: [^false].
       ops do: [
-          :op |
-          (op tryDo: n target: tgt) ifNotNil:
-          [:it|(self canSolveFrom: idx - 1 target: it with: ops) ifTrue: [^true]]].
+          :op | n1 := op tryDo: n target: tgt.
+          n1 ifNotNil: [
+              ok := self canSolveFrom: idx - 1 target: n1 with: ops.
+              ok ifTrue: [^true] ]].
       ^false ]
     canSolveWith: ops [^self canSolveFrom: numbers size target: target with: ops]
 ]
 
 Equation class extend [
     parse: line
-    [ ^(line tokenize: ': ') letArrayInBlock:
-           [ :target :numbers |
-             Equation new target: target asNumber;
-                     numbers: ((numbers tokenize: ' ') collect: [:it|it asNumber]) ] ]
+    [^(line tokenize: ': ') letArrayInBlock: [
+         :target :numbers |
+         Equation new target: target asNumber;
+                 numbers: ((numbers tokenize: ' ')
+                               collect: [:it|it asNumber])]]
 ]
 
 AOC input: [ stdin toLines collect: [:line | Equation parse: line] ];
@@ -42,6 +47,6 @@ AOC input: [ stdin toLines collect: [:line | Equation parse: line] ];
     part2: {CatOp new. MulOp new. AddOp new};
     result: [ :eqns :part |
               eqns chain select: [:eqn | eqn canSolveWith: part];
-                    collect: [:it|it testValue];
+                    collect: [:it | it testValue];
                     sum ];
     finish.
diff --git a/days/utils.st b/days/utils.st
index b5883d2..8112623 100644
--- a/days/utils.st
+++ b/days/utils.st
@@ -254,3 +254,30 @@ Object subclass: Grid [
 
     printOn: st [ rows do: [ :r | st << r; nl ] ]
 ]
+
+Integer extend [
+    ceilingDiv: denom [ ^((self - 1) // denom) + 1 ]
+
+    "The original implementation was incorrect. Here is the correct code:"
+    ceilingLog: radix [
+        "Answer (self log: radix) ceiling. Optimized to answer an integer."
+
+        <category: 'math methods'>
+        | me answer |
+        self < self zero ifTrue:
+             [^self arithmeticError: 'cannot extract logarithm of a negative number'].
+        radix <= radix unity ifTrue: 
+              [radix <= radix zero 
+                     ifTrue: [^self arithmeticError: 'base of a logarithm cannot be negative'].
+               radix = radix unity 
+                     ifTrue: [^self arithmeticError: 'base of a logarithm cannot be 1'].
+               ^(self floorLog: radix reciprocal) negated].
+        radix isInteger ifFalse: [^(radix coerce: self) ceilingLog: radix].
+        me := self.
+        answer := 1.
+        [me > radix] whileTrue: 
+            [me := me ceilingDiv: radix. "originally: me // radix."
+             answer := answer + 1].
+        ^answer
+    ]
+]