diff --git a/src/aoc2025/Day09.kt b/src/aoc2025/Day09.kt
index 4931905..6a9044a 100644
--- a/src/aoc2025/Day09.kt
+++ b/src/aoc2025/Day09.kt
@@ -3,6 +3,7 @@ package aoc2025
 import println
 import readInput
 import splitInts
+import java.util.*
 import kotlin.math.abs
 
 /*
@@ -27,38 +28,35 @@ fun main() {
         var maxArea = 0L
         for (i1 in 0 until coords.size step 2) {
             for (i2 in i1 + 2 until coords.size step 2) {
-                maxArea = ((abs(coords[i1][0] - coords[i2][0]) + 1).toLong() * (abs(coords[i1][1] - coords[i2][1]) + 1).toLong()).coerceAtLeast(maxArea)
+                maxArea =
+                    ((abs(coords[i1][0] - coords[i2][0]) + 1).toLong() * (abs(coords[i1][1] - coords[i2][1]) + 1).toLong()).coerceAtLeast(
+                        maxArea
+                    )
             }
         }
         return maxArea
     }
 
-    fun intersects(coords: List<List<Int>>, x1: Int, y1: Int, x2: Int, y2: Int): Boolean {
-        for (z1 in 0 until coords.size) {
-            val z2 = if (z1 != coords.size - 1) z1 + 1 else 0
-            if (coords[z1][0] == coords[z2][0]) {
-                // vertical
-                val miny = coords[z1][1].coerceAtMost(coords[z2][1])
-                val maxy = coords[z1][1].coerceAtLeast(coords[z2][1])
-                if (coords[z1][0] > x1 && coords[z1][0] < x2 &&
-                    (miny.coerceAtLeast(y1) < maxy.coerceAtMost(y2))
-                )
-                    return true
-            } else {
-                // horizontal
-                val minx = coords[z1][0].coerceAtMost(coords[z2][0])
-                val maxx = coords[z1][0].coerceAtLeast(coords[z2][0])
-                if (coords[z1][1] > y1 && coords[z1][1] < y2 &&
-                    (minx.coerceAtLeast(x1) < maxx.coerceAtMost(x2))
-                )
-                    return true
-            }
-        }
-        return false
-    }
+    fun intersectsRanges(set: TreeMap<Int, ArrayList<IntRange>>, x1: Int, y1: Int, x2: Int, y2: Int) =
+        set.subMap(y1 + 1, y2).values.any { it.any { it.first < x2 && it.last > x1 } }
 
     fun part2(input: List<String>): Long {
         val coords = input.map { it.splitInts(",") }
+        val xSpans = TreeMap<Int, ArrayList<IntRange>>()
+        val ySpans = TreeMap<Int, ArrayList<IntRange>>()
+        for (i1 in 0 until coords.size) {
+            val i2 = if (i1 != coords.size - 1) i1 + 1 else 0
+            if (coords[i1][1] == coords[i2][1]) {
+                xSpans.getOrPut(coords[i1][1]) { ArrayList<IntRange>() }.add(
+                    IntRange(coords[i1][0].coerceAtMost(coords[i2][0]), coords[i1][0].coerceAtLeast(coords[i2][0]))
+                )
+            } else {
+                ySpans.getOrPut(coords[i1][0]) { ArrayList<IntRange>() }.add(
+                    IntRange(coords[i1][1].coerceAtMost(coords[i2][1]), coords[i1][1].coerceAtLeast(coords[i2][1]))
+                )
+            }
+        }
+
         var maxArea = 0L
         for (i1 in 0 until coords.size step 2) {
             for (i2 in i1 + 2 until coords.size step 2) {
@@ -68,9 +66,10 @@ fun main() {
                 val y2 = coords[i1][1].coerceAtLeast(coords[i2][1])
 
                 val area = ((x2 - x1 + 1).toLong() * (y2 - y1 + 1).toLong())
-                if (area > maxArea) {
-                    if (!intersects(coords, x1, y1, x2, y2))
-                        maxArea = area
+                if (area > maxArea &&
+                    !(intersectsRanges(xSpans, x1, y1, x2, y2) || intersectsRanges(ySpans, y1, x1, y2, x2))
+                ) {
+                    maxArea = area
                 }
             }
         }