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Restored "clever" method for day 9. Not much faster, though.

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Change-Id: I8ced811be7415db8281a13f1f8200192b05914e2
This commit is contained in:
Chris Hodges 2025-12-09 13:06:28 +01:00
parent d2044f2d6a
commit caf82dd7a9
1 changed files with 26 additions and 27 deletions
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51
src/aoc2025/Day09.kt
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@ -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) {
@ -68,8 +66,9 @@ 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))
if (area > maxArea &&
!(intersectsRanges(xSpans, x1, y1, x2, y2) || intersectsRanges(ySpans, y1, x1, y2, x2))
) {
maxArea = area
}
}