Optimize 2024 day 20 part 2 by not creating set

All cheats are unique by construction.

Author: sim642

src/main/scala/eu/sim642/adventofcode2024/Day20.scala

@@ -28,17 +28,15 @@ object Day20 {
   trait Part {
     val maxCheat: Int
 
-    def findCheats(grid: Grid[Char]): Set[Cheat] = {
+    def findCheats(grid: Grid[Char]): Iterable[Cheat] = {
       val forwardSearch = gridGraphSearch(grid, 'S', 'E')
       val forwardResult = BFS.search(forwardSearch)
       val backwardSearch = gridGraphSearch(grid, 'E', 'S')
       val backwardResult = BFS.search(backwardSearch)
 
       val noCheatDistance = forwardResult.target.get._2
 
-      // TODO: optimize
-
-      (for {
+      for {
         (row, y) <- grid.view.zipWithIndex
         (cell, x) <- row.view.zipWithIndex
         if cell != '#'
@@ -55,7 +53,7 @@ object Day20 {
         cheatDistance = forwardResult.distances(start) + (startCheat + endCheat) + backwardResult.distances(end)
         //if cheatDistance <= noCheatDistance
         save = noCheatDistance - cheatDistance
-      } yield Cheat(start, end, save)).toSet
+      } yield Cheat(start, end, save)
     }
 
     def countGoodCheats(grid: Grid[Char]): Int = findCheats(grid).count(_.save >= 100)

src/test/scala/eu/sim642/adventofcode2024/Day20Test.scala

@@ -60,7 +60,7 @@ class Day20Test extends AnyFunSuite {
     assert(cheats(76) == 3)
   }
 
-  test("Part 2 input answer") { // TODO: optimize (~4.3s)
+  test("Part 2 input answer") {
     assert(Part2.countGoodCheats(parseGrid(input)) == 1011325)
   }
 }