Day 5: part 1 cleanup

Author: horothesun

src/main/scala/Day05.scala

@@ -5,7 +5,7 @@ import cats.syntax.all.*
 
 object Day05:
 
-  case class Page(n: Int)
+  case class Page(n: Int) derives Eq
 
   object Page:
     def parse(s: String): Option[Page] = s.toIntOption.map(Page.apply)
@@ -38,9 +38,13 @@ object Day05:
       as.reverse.foldLeft(List(List.empty[A]))((l, a) => if a == sep then List.empty :: l else (a :: l.head) :: l.tail)
 
   case class Input(rules: NonEmptyList[OrderRule], updates: NonEmptyList[Update]):
+
+    def filteredRules(update: Update): List[OrderRule] =
+      rules.filter(r => update.pages.contains_(r.before) && update.pages.contains_(r.after))
+
     def correctlyOrderedUpdatesMiddlePageSum: Int =
       updates
-        .collect(u => u.firstViolatedOrderRules(rules) match { case None => u })
+        .collect(u => filteredRules(u).toNel.flatMap(u.firstViolatedOrderRules) match { case None => u })
         .foldMap(_.middlePage.n)
 
   object Input:

src/test/scala/Day05Suite.scala

@@ -46,49 +46,63 @@ class Day05Suite extends ScalaCheckSuite:
       Page(1)
     )
 
-  test("first violated order rule for small input's first update is None"):
+  test("first violated order rule for small input's 1st update is None"):
     assertEquals(
-      Input.parse(smallInput).flatMap(input => input.updates.head.firstViolatedOrderRules(input.rules)),
+      for {
+        input <- Input.parse(smallInput)
+        firstPage = input.updates.head
+        orderRule <- firstPage.firstViolatedOrderRules(input.rules)
+      } yield orderRule,
       None
     )
 
-  test("first violated order rule for small input's second update is None"):
+  test("first violated order rule for small input's 2nd update is None"):
     assertEquals(
-      Input
-        .parse(smallInput)
-        .flatMap(input => input.updates.toNev.get(1).flatMap(_.firstViolatedOrderRules(input.rules))),
+      for {
+        input <- Input.parse(smallInput)
+        secondPage <- input.updates.toNev.get(1)
+        orderRule <- secondPage.firstViolatedOrderRules(input.rules)
+      } yield orderRule,
       None
     )
 
-  test("first violated order rule for small input's third update is None"):
+  test("first violated order rule for small input's 3rd update is None"):
     assertEquals(
-      Input
-        .parse(smallInput)
-        .flatMap(input => input.updates.toNev.get(2).flatMap(_.firstViolatedOrderRules(input.rules))),
+      for {
+        input <- Input.parse(smallInput)
+        thirdPage <- input.updates.toNev.get(2)
+        orderRule <- thirdPage.firstViolatedOrderRules(input.rules)
+      } yield orderRule,
       None
     )
 
-  test("first violated order rule for small input's fourth update is 97|75"):
+  test("first violated order rule for small input's 4th update is 97|75"):
     assertEquals(
-      Input
-        .parse(smallInput)
-        .flatMap(input => input.updates.toNev.get(3).flatMap(_.firstViolatedOrderRules(input.rules))),
+      for {
+        input <- Input.parse(smallInput)
+        fourthPage <- input.updates.toNev.get(3)
+        orderRule <- fourthPage.firstViolatedOrderRules(input.rules)
+      } yield orderRule,
       OrderRule(before = Page(97), after = Page(75)).some
     )
 
-  test("first violated order rule for small input's fifth update is 29|13"):
+  test("first violated order rule for small input's 5th update is 29|13"):
     assertEquals(
-      Input
-        .parse(smallInput)
-        .flatMap(input => input.updates.toNev.get(4).flatMap(_.firstViolatedOrderRules(input.rules))),
+      for {
+        input <- Input.parse(smallInput)
+        fifthPage <- input.updates.toNev.get(4)
+        orderRule <- fifthPage.firstViolatedOrderRules(input.rules)
+      } yield orderRule,
       OrderRule(before = Page(29), after = Page(13)).some
     )
 
-  test("first violated order rule for small input's sixth update is 75|13"):
+  test("first violated order rule for small input's 6th update is 75|13"):
     assertEquals(
-      Input
-        .parse(smallInput)
-        .flatMap(input => input.updates.toNev.get(5).flatMap(_.firstViolatedOrderRules(input.rules))),
+      for {
+        input <- Input.parse(smallInput)
+        sixthPage <- input.updates.toNev.get(5)
+        orderRule <- sixthPage.firstViolatedOrderRules(input.rules)
+      } yield orderRule,
       OrderRule(before = Page(75), after = Page(13)).some
     )