Day 11.

src/aoc2024/Day13.kt

@@ -82,7 +82,7 @@ Prize: X=18641, Y=10279
 
             // Linear Diophantine equations
             /* The simplest linear Diophantine equation takes the form
-               a*x + b*x = c
+               a*x + b*y = c
                where a, b and c are given integers.
                The solutions are described by the following theorem:
                This Diophantine equation has a solution (where x and y are integers),

src/aoc2025/Day10.kt

@@ -1,8 +1,10 @@
 package aoc2025
 
+import calcCanonicalPrimesSieveOfEratosthenes
 import println
 import readInput
 import splitInts
+import java.math.BigInteger
 import java.util.*
 
 /*
@@ -29,7 +31,6 @@ fun main() {
             val toggles =
                 stuff.drop(1).dropLast(1)
                     .map { it.removeSurrounding("(", ")").splitInts(",").fold(0) { acc, v -> acc + (1 shl v) } }
-                    .sortedByDescending { it.countOneBits() }
                     .toIntArray()
             val joltages = stuff.last().removeSurrounding("{", "}").splitInts(",").toIntArray()
             machines.add(Machine(machSize, target, toggles, joltages))
@@ -41,23 +42,17 @@ fun main() {
         val machines = parse(input)
         var sumButts = 0
         for (m in machines) {
-            val pq = LinkedList<Pair<Int, Int>>()
-            val killArray = BooleanArray(1 shl m.size)
-            pq.add(0 to 0)
-            out@ while (pq.isNotEmpty()) {
-                val (v, bi) = pq.poll()
-                for (t in m.toggles) {
-                    val nv = v xor t
-                    if (nv == m.target) {
-                        sumButts += bi + 1
-                        break@out
-                    }
-                    if (!killArray[nv]) {
-                        killArray[v] = true
-                        pq.add(nv to bi + 1)
-                    }
+            // look at which different possible sets of toggles need to be pressed to result in the target number
+            // pressing an even time will cancel out the effect, so only look what happens if you press once
+            var minPresses = Int.MAX_VALUE
+            for (tm in 1 until (1 shl m.toggles.size)) {
+                val odds = m.toggles.filterIndexed { i, v -> (1 shl i) and tm != 0 }
+                val result = odds.fold(0) { acc, iv -> acc xor iv }
+                if (result == m.target) {
+                    minPresses = minPresses.coerceAtMost(odds.size)
                 }
             }
+            sumButts += minPresses
         }
         return sumButts
     }
@@ -99,11 +94,69 @@ fun main() {
     fun part2(input: List<String>): Int {
         val machines = parse(input)
 
+        val primes = calcCanonicalPrimesSieveOfEratosthenes(10000)
+        var sumButts = 0
+        for (m in machines) {
+            println()
+            val maxJoltage = m.joltage.max()
+            val numBits = 32 - maxJoltage.countLeadingZeroBits()
+            val bigTarget = m.joltage.foldIndexed(BigInteger.ZERO) { index, acc, i -> acc.plus(BigInteger.valueOf(i.toLong()).shiftLeft(numBits * index)) }
+            val bigToggles = ArrayList<Pair<BigInteger, BigInteger>>()
+            for (t in m.toggles) {
+                var tt = t
+                var bigToggle = BigInteger.ZERO
+                var shift = 0
+                while (tt > 0) {
+                    if (tt and 1 != 0) {
+                        bigToggle = bigToggle.plus(BigInteger.ONE.shiftLeft(shift))
+                    }
+                    shift += numBits
+                    tt = tt shr 1
+                }
+                val maxValue = bigTarget.divide(bigToggle).and(BigInteger.ONE.shiftLeft(numBits).minus(BigInteger.ONE)).toInt() + 1
+                println(maxValue)
+                if (maxValue > 0) {
+                    bigToggles.add(bigToggle to BigInteger.valueOf(maxValue.toLong()))
+                }
+            }
+            var presses = BigInteger.ONE
+            var leastFingers = Integer.MAX_VALUE
+            val maxPresses = bigToggles.fold(BigInteger.ONE) { acc, bt -> acc.multiply(bt.second) }
+            while (presses <= maxPresses) {
+                var pe = 0
+                var pr = presses
+                var bt = bigTarget
+                var fingers = 0
+                while (pe < bigToggles.size && pr > BigInteger.ZERO) {
+                    val f = pr.mod(bigToggles[pe].second)
+                    fingers += f.toInt()
+                    if (fingers > leastFingers) break
+                    bt = bt.minus(bigToggles[pe].first.multiply(f))
+                    if (bt <= BigInteger.ZERO) break
+                    pr = pr.divide(bigToggles[pe].second)
+                    pe++
+                }
+                if (bt == BigInteger.ZERO) {
+                    leastFingers = leastFingers.coerceAtMost(fingers)
+                    break
+                }
+                presses = presses.plus(BigInteger.ONE)
+            }
+            println(leastFingers)
+            sumButts += leastFingers
+        }
+        return sumButts
+    }
+
+    fun part2old(input: List<String>): Int {
+        val machines = parse(input)
+
         var sumButts = 0
         for (m in machines) {
             // generate toggles and calculate the global maximum of toggle presses for this toggle
             val toggles = m.toggles.mapIndexed { i, t ->
-                Toggle(i,
+                Toggle(
+                    i,
                     t,
                     max = IntRange(0, m.size).filter { b -> t and (1 shl b) != 0 }.minOf { m.joltage[it] })
             }
@@ -128,19 +181,13 @@ fun main() {
                 v.min = minT
             }
 
-            // iterate over the possible odd sets
             var minPushes = Int.MAX_VALUE
             val jolts = m.joltage.copyOf()
             val pressCount = IntArray(m.toggles.size)
 
             // press all buttons regarding their minimal count (if any)
             for (t in toggles) {
-                if (pressCount[t.idx] + t.min > t.max || !applyJoltage(
-                        jolts,
-                        t,
-                        times = t.min
-                    )
-                ) throw IllegalStateException()
+                if (pressCount[t.idx] + t.min > t.max || !applyJoltage(jolts, t, times = t.min)) throw IllegalStateException()
                 pressCount[t.idx] += t.min
             }
             // this is the starting point for the exhaustive search
@@ -157,7 +204,7 @@ fun main() {
                 }
                 for (t in toggles) {
                     if (tc[t.idx] + 2 <= t.max) {
-                        val maxTimes = findMaxButtonPresses(j, t)
+                        val maxTimes = 1//findMaxButtonPresses(j, t)
                         if (maxTimes > 0) {
                             val nj = j.copyOf()
                             if (applyJoltage(nj, t, maxTimes)) {
@@ -184,7 +231,7 @@ fun main() {
     val testInputPart2Result = part2(testInput)
     println("Part 2 Test: $testInputPart2Result")
     check(testInputPart1Result == 7)
-    //check(testInputPart2Result == 33)
+    check(testInputPart2Result == 33)
 
     val input = readInput("aoc2025/Day10")
     part1(input).println()

src/aoc2025/Day11.kt

@@ -0,0 +1,111 @@
+package aoc2025
+
+import println
+import readInput
+
+/*
+--- Day 11: Reactor ---
+https://adventofcode.com/2025/day/11
+*/
+fun main() {
+
+    val inlineTestInput = """
+aaa: you hhh
+you: bbb ccc
+bbb: ddd eee
+ccc: ddd eee fff
+ddd: ggg
+eee: out
+fff: out
+ggg: out
+hhh: ccc fff iii
+iii: out
+"""
+
+    val inlineTestInput2 = """
+svr: aaa bbb
+aaa: fft
+fft: ccc
+bbb: tty
+tty: ccc
+ccc: ddd eee
+ddd: hub
+hub: fff
+eee: dac
+dac: fff
+fff: ggg hhh
+ggg: out
+hhh: out
+"""
+
+    data class Node(val name: String, val children: Set<Node>)
+
+    fun rec(children: HashMap<String, MutableSet<String>>, p: String, visited: MutableSet<String>): Int {
+        if (p == "out") return 1
+        visited.add(p)
+        val res = children[p]!!.sumOf { rec(children, it, visited) }
+        visited.remove(p)
+        return res
+    }
+
+    fun parseInput(input: List<String>): HashMap<String, MutableSet<String>> {
+        val children = HashMap<String, MutableSet<String>>()
+        for (i in input) {
+            val (n, chs) = i.split(": ")
+            val ch = chs.split(" ")
+            children.getOrPut(n) { HashSet() }.addAll(ch)
+        }
+        return children
+    }
+
+    fun part1(input: List<String>): Int {
+        val children = parseInput(input)
+
+        return rec(children, "you", HashSet())
+    }
+
+    fun rec2(
+        children: HashMap<String, MutableSet<String>>,
+        p: String,
+        stop: String,
+        visited: MutableSet<String> = HashSet(),
+        memo: HashMap<String, Long> = HashMap()
+    ): Long {
+        if (p == stop) return 1L
+        val memoVal = memo[p]
+        if (memoVal != null) return memoVal
+        visited.add(p)
+        val res = children[p]?.sumOf { rec2(children, it, stop, visited, memo) } ?: 0L
+        visited.remove(p)
+        memo[p] = res
+        return res
+    }
+
+    fun part2(input: List<String>): Long {
+        val children = parseInput(input)
+
+        val srvToDac = rec2(children, "svr", "dac")
+        val dacToFft = rec2(children, "dac", "fft")
+        val fftToOut = rec2(children, "fft", "out")
+        val srvToFft = rec2(children, "svr", "fft")
+        val fftToDac = rec2(children, "fft", "dac")
+        val dacToOut = rec2(children, "dac", "out")
+
+        return srvToDac * dacToFft * fftToOut + srvToFft * fftToDac * dacToOut
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    val testInput2 = inlineTestInput2.trim().reader().readLines()
+    //val testInput = readInput("aoc2025/Day11_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput2)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 5)
+    check(testInputPart2Result == 2L)
+
+    val input = readInput("aoc2025/Day11")
+    part1(input).println()
+    part2(input).println()
+}