From 52af74ecd5cf193cb84ec5e3a43ddfd773335a8e Mon Sep 17 00:00:00 2001
From: chrisly42 <chrisly@platon42.de>
Date: Mon, 8 Dec 2025 07:04:34 +0100
Subject: [PATCH] Day 8: Use priority queue.

---
 src/aoc2025/Day08.kt | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/aoc2025/Day08.kt b/src/aoc2025/Day08.kt
index 736c671..1a62579 100644
--- a/src/aoc2025/Day08.kt
+++ b/src/aoc2025/Day08.kt
@@ -3,6 +3,7 @@ package aoc2025
 import println
 import readInput
 import splitInts
+import java.util.*
 import kotlin.math.sqrt
 
 /*
@@ -54,16 +55,15 @@ fun main() {
         return false
     }
 
-    // priority queue would have been more efficient... who cares
-    fun createDistances(nodes: Array<IntArray>): Iterable<Pair<Pair<Int, Int>, Float>> {
-        val distances = ArrayList<Pair<Pair<Int, Int>, Float>>()
+    // having an oct-tree might speed up things here, so we skip far distances
+    fun createDistances(nodes: Array<IntArray>): PriorityQueue<Pair<Pair<Int, Int>, Float>> {
+        val distances = PriorityQueue<Pair<Pair<Int, Int>, Float>>(nodes.size * nodes.size / 2, Comparator.comparing { it.second })
         for (i1 in 0 until nodes.size) {
             for (i2 in i1 + 1 until nodes.size) {
                 val d = dist(nodes[i1], nodes[i2])
                 distances.add((i1 to i2) to d)
             }
         }
-        distances.sortBy { it.second }
         return distances
     }
 
@@ -74,8 +74,8 @@ fun main() {
         val n = nodes.size
         var numCircuits = 0
         val unionFindParentArray = IntArray(n) { it }
-        for (d in distances) {
-            val (n1, n2) = d.first
+        while (distances.isNotEmpty()) {
+            val (n1, n2) = distances.remove().first
             union(unionFindParentArray, n1, n2)
             numCircuits++
             if (numCircuits == numConnections) break
@@ -95,8 +95,8 @@ fun main() {
         val n = nodes.size
         var numCircuits = 1
         val unionFindParentArray = IntArray(n) { it }
-        for (d in distances) {
-            val (n1, n2) = d.first
+        while (distances.isNotEmpty()) {
+            val (n1, n2) = distances.remove().first
             if (union(unionFindParentArray, n1, n2)) {
                 numCircuits++
                 if (numCircuits == n) {