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Day 7 Part 2 optimized to 666ms (instead of around 3000ms).

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This commit is contained in:
Chris Hodges 2024-12-07 07:13:32 +01:00
parent ea9f44a12c
commit 8d492486fb
1 changed files with 12 additions and 3 deletions
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15
src/aoc2024/Day07.kt
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@ -4,7 +4,6 @@ import println
import readInput import readInput
import splitLongs import splitLongs
import kotlin.math.pow import kotlin.math.pow
import kotlin.math.roundToLong
/* /*
--- Day 7: Bridge Repair --- --- Day 7: Bridge Repair ---
@ -66,6 +65,16 @@ fun main() {
return sum return sum
} }
val powTenTable = generateSequence(1L) { it * 10L }.take(10).toList().toLongArray()
val powThreeTable = generateSequence(1) { it * 3 }.take(12).toList().toIntArray()
fun fastCeilLog10(n: Long): Int {
for (i in 1 until 9) {
if (powTenTable[i] > n) return i
}
return -1
}
fun part2(input: List<String>): Long { fun part2(input: List<String>): Long {
var sum = 0L var sum = 0L
for (i in input) { for (i in input) {
@ -75,10 +84,10 @@ fun main() {
val combs = 3.0.pow(ops.size - 1).toInt() val combs = 3.0.pow(ops.size - 1).toInt()
for (t in 0 until combs) { for (t in 0 until combs) {
val res = ops.reduceIndexed { index, acc, l -> val res = ops.reduceIndexed { index, acc, l ->
when ((t / (3.0.pow(index - 1).toInt())) % 3) { when ((t / powThreeTable[index - 1]) % 3) {
0 -> acc + l 0 -> acc + l
1 -> acc * l 1 -> acc * l
2 -> acc * (10.0.pow(l.toString().length.toDouble()).roundToLong()) + l 2 -> acc * powTenTable[fastCeilLog10(l)] + l
else -> throw IllegalArgumentException() else -> throw IllegalArgumentException()
} }
} }