Try reducing duplicate work

ephemient · Dec 16, 2023 · c366bba · c366bba
1 parent 1137017
commit c366bba
Showing 1 changed file with 30 additions and 8 deletions.
diff --git a/kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day16.kt b/kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day16.kt
@@ -3,7 +3,7 @@ package com.github.ephemient.aoc2023
 class Day16(input: String) {
     private val input = input.lines().filter { it.isNotEmpty() }
 
-    private fun fill(y: Int, x: Int, d: Direction): Int {
+    private fun fill(y: Int, x: Int, d: Direction, todo: MutableSet<Pair<IntPair, Direction>>): Int {
         val stack = mutableListOf(y to x to d)
         val visited = stack.toMutableSet()
         while (true) {
@@ -13,23 +13,45 @@ class Day16(input: String) {
                 if (p2.first in input.indices && p2.second in input[p2.first].indices) {
                     val next = p2 to d2
                     visited.add(next) && stack.add(next)
+                } else {
+                    todo.remove(p1 to -d1)
                 }
             }
         }
         return visited.mapTo(mutableSetOf()) { it.first }.size
     }
 
-    fun part1(): Int = fill(0, 0, Direction.R)
+    fun part1(): Int = fill(0, 0, Direction.R, mutableSetOf())
 
-    fun part2(): Int = maxOf(
-        input.indices.maxOf { fill(it, 0, Direction.R) },
-        input.first().indices.maxOf { fill(0, it, Direction.D) },
-        input.indices.maxOf { fill(it, input[it].lastIndex, Direction.L) },
-        input.last().indices.maxOf { fill(input.lastIndex, it, Direction.U) },
-    )
+    fun part2(): Int {
+        var max = 0
+        val todo = mutableSetOf<Pair<IntPair, Direction>>()
+        for (x in 0..input.first().lastIndex) todo.add(0 to x to Direction.D)
+        for ((y, line) in input.withIndex()) {
+            todo.add(y to 0 to Direction.R)
+            todo.add(y to line.lastIndex to Direction.L)
+        }
+        for (x in 0..input.last().lastIndex) todo.add(input.lastIndex to x to Direction.U)
+        while (true) {
+            val iterator = todo.iterator()
+            if (!iterator.hasNext()) break
+            val (pos, d) = iterator.next()
+            iterator.remove()
+            max = maxOf(max, fill(pos.first, pos.second, d, todo))
+        }
+        return max
+    }
 
     private enum class Direction {
         U, L, D, R,
+        ;
+
+        operator fun unaryMinus(): Direction = when (this) {
+            U -> D
+            L -> R
+            D -> U
+            R -> L
+        }
     }
 
     companion object {