From a8b68b19b906b640b41927e91ef87ef5f44e7f4f Mon Sep 17 00:00:00 2001
From: Matej Focko <mfocko@redhat.com>
Date: Fri, 24 Dec 2021 21:48:29 +0100
Subject: [PATCH] day(24): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>
---
 src/year2021/day24/Day24.kt        | 46 ++++++++++++++++++++++++++++++
 src/year2021/day24/binary.txt      | 11 +++++++
 src/year2021/day24/negate.txt      |  2 ++
 src/year2021/day24/three_times.txt |  4 +++
 4 files changed, 63 insertions(+)
 create mode 100644 src/year2021/day24/Day24.kt
 create mode 100644 src/year2021/day24/binary.txt
 create mode 100644 src/year2021/day24/negate.txt
 create mode 100644 src/year2021/day24/three_times.txt

diff --git a/src/year2021/day24/Day24.kt b/src/year2021/day24/Day24.kt
new file mode 100644
index 0000000..0ff4434
--- /dev/null
+++ b/src/year2021/day24/Day24.kt
@@ -0,0 +1,46 @@
+package year2021.day24
+
+import readInput
+
+data class Parameter(val remainder: Long, val divisor: Long, val addition: Long)
+
+fun solver(range: LongProgression, parameters: List<Parameter>): Long {
+    val cache: MutableMap<Triple<Int, Long, Long>, Long?> = mutableMapOf()
+
+    fun solveAlternative(i: Int, w: Long, z: Long, overall: Long = 0): Long? {
+        val cacheKey = Triple(i, w, z)
+        if (cacheKey in cache) {
+            return cache[cacheKey];
+        }
+
+        val (remainder, divisor, addition) = parameters[i]
+        val x = if (((z % 26) + remainder) != w) 1 else 0
+
+        val newZ = z / divisor * (25 * x + 1) + (w + addition) * x
+        val result = when (i) {
+            13 -> if (newZ == 0L) overall else null
+            else -> range.firstNotNullOfOrNull {
+                solveAlternative(i + 1, it, newZ, overall * 10 + it)
+            }
+        }
+
+        cache[cacheKey] = result
+        return result
+    }
+
+    return range.firstNotNullOf { solveAlternative(0, it, 0, it) }
+}
+
+fun part1(parameters: List<Parameter>): Long = solver(9L downTo 1L, parameters)
+fun part2(parameters: List<Parameter>): Long = solver(1L..9L, parameters)
+
+fun List<String>.toParameters(): List<Parameter> = this.chunked(18).map {
+    val (rem, div, add) = listOf(it[5], it[4], it[15]).map { it.split(" ")[2].toLong() }
+    Parameter(rem, div, add)
+}
+
+fun main() {
+    val parameters = readInput(24, "input").toParameters()
+    println(part1(parameters))
+    println(part2(parameters))
+}
diff --git a/src/year2021/day24/binary.txt b/src/year2021/day24/binary.txt
new file mode 100644
index 0000000..b5b5961
--- /dev/null
+++ b/src/year2021/day24/binary.txt
@@ -0,0 +1,11 @@
+inp w
+add z w
+mod z 2
+div w 2
+add y w
+mod y 2
+div w 2
+add x w
+mod x 2
+div w 2
+mod w 2
\ No newline at end of file
diff --git a/src/year2021/day24/negate.txt b/src/year2021/day24/negate.txt
new file mode 100644
index 0000000..10afe48
--- /dev/null
+++ b/src/year2021/day24/negate.txt
@@ -0,0 +1,2 @@
+inp x
+mul x -1
\ No newline at end of file
diff --git a/src/year2021/day24/three_times.txt b/src/year2021/day24/three_times.txt
new file mode 100644
index 0000000..95b52cf
--- /dev/null
+++ b/src/year2021/day24/three_times.txt
@@ -0,0 +1,4 @@
+inp z
+inp x
+mul z 3
+eql z x
\ No newline at end of file