134 lines
4.7 KiB
Kotlin
134 lines
4.7 KiB
Kotlin
package aoc2025
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import println
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import readInput
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import splitInts
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import java.util.*
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import kotlin.math.abs
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/*
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--- Day 9: Movie Theater ---
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https://adventofcode.com/2025/day/9
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*/
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fun main() {
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val inlineTestInput = """
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7,3
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7,1
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11,1
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11,7
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9,7
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9,5
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2,5
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2,3
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"""
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fun part1(input: List<String>): Long {
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val coords = input.map { it.splitInts(",") }
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var maxArea = 0L
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for (i1 in 0 until coords.size step 2) {
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for (i2 in i1 + 2 until coords.size step 2) {
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maxArea = ((abs(coords[i1][0] - coords[i2][0]) + 1).toLong() * (abs(coords[i1][1] - coords[i2][1]) + 1).toLong()).coerceAtLeast(maxArea)
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}
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}
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return maxArea
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}
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fun findRanges(set: TreeMap<Int, ArrayList<IntRange>>, x1: Int, y1: Int, x2: Int, y2: Int): Boolean {
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var it = set.ceilingEntry(y1)
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while (it != null && it.key <= y2) {
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val xRanges = it.value.filter { it.first() >= x1 && it.last() <= x2 }
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if (it.key != y1 && it.key != y2 && xRanges.size > 0) return false
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if ((it.key == y1 || it.key == y2) && xRanges.size > 1) return false
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// Java TreeMap is crap -- I would like to iterate from first entry to last
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it = set.ceilingEntry(it.key + 1)
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}
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return true
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}
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fun intersects(coords: List<List<Int>>, x1: Int, y1: Int, x2: Int, y2: Int): Boolean {
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for (z1 in 0 until coords.size) {
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val z2 = if (z1 != coords.size - 1) z1 + 1 else 0
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if (coords[z1][0] == coords[z2][0]) {
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// vertical
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val miny = coords[z1][1].coerceAtMost(coords[z2][1])
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val maxy = coords[z1][1].coerceAtLeast(coords[z2][1])
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if (coords[z1][0] > x1 && coords[z1][0] < x2 &&
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(miny.coerceAtLeast(y1) < maxy.coerceAtMost(y2))
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)
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return true
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} else {
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// horizontal
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val minx = coords[z1][0].coerceAtMost(coords[z2][0])
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val maxx = coords[z1][0].coerceAtLeast(coords[z2][0])
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if (coords[z1][1] > y1 && coords[z1][1] < y2 &&
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(minx.coerceAtLeast(x1) < maxx.coerceAtMost(x2))
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)
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return true
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}
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}
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return false
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}
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fun part2(input: List<String>): Long {
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val coords = input.map { it.splitInts(",") }
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val xSpans = TreeMap<Int, ArrayList<IntRange>>()
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val ySpans = TreeMap<Int, ArrayList<IntRange>>()
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for (i1 in 0 until coords.size) {
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val i2 = if (i1 != coords.size - 1) i1 + 1 else 0
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if (i1 and 1 == 1) {
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xSpans.getOrPut(coords[i1][1]) { ArrayList<IntRange>() }.add(
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IntRange(
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coords[i1][0].coerceAtMost(coords[i2][0]),
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coords[i1][0].coerceAtLeast(coords[i2][0])
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)
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)
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} else {
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ySpans.getOrPut(coords[i1][0]) { ArrayList<IntRange>() }.add(
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IntRange(
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coords[i1][1].coerceAtMost(coords[i2][1]),
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coords[i1][1].coerceAtLeast(coords[i2][1])
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)
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)
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}
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}
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//xSpans.values.forEach { it.sortBy { it.first } }
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//ySpans.values.forEach { it.sortBy { it.first } }
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var maxArea = 0L
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for (i1 in 0 until coords.size step 1) {
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for (i2 in i1 + 1 until coords.size step 1) {
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val x1 = coords[i1][0].coerceAtMost(coords[i2][0])
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val x2 = coords[i1][0].coerceAtLeast(coords[i2][0])
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val y1 = coords[i1][1].coerceAtMost(coords[i2][1])
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val y2 = coords[i1][1].coerceAtLeast(coords[i2][1])
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if (x1 == x2 || y1 == y2) continue
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val area = ((x2 - x1 + 1).toLong() * (y2 - y1 + 1).toLong())
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if (area > maxArea) {
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// if (!findRanges(xSpans, x1, y1, x2, y2) ||
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// !findRanges(ySpans, y1, x1, y2, x2)
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// ) continue
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if (!intersects(coords, x1, y1, x2, y2))
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maxArea = area
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}
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}
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}
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return maxArea
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}
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// test if implementation meets criteria from the description, like:
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val testInput = inlineTestInput.trim().reader().readLines()
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//val testInput = readInput("aoc2025/Day09_test")
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val testInputPart1Result = part1(testInput)
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println("Part 1 Test: $testInputPart1Result")
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val testInputPart2Result = part2(testInput)
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println("Part 2 Test: $testInputPart2Result")
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check(testInputPart1Result == 50L)
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check(testInputPart2Result == 24L)
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val input = readInput("aoc2025/Day09")
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part1(input).println()
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part2(input).println()
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}
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