From f494b763cf4265ea68d7381678319906139da3f9 Mon Sep 17 00:00:00 2001
From: chrisly42 <chrisly@platon42.de>
Date: Sat, 21 Dec 2024 12:26:08 +0100
Subject: [PATCH] Day 21 :-(

---
 src/aoc2024/Day21.kt | 141 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 141 insertions(+)
 create mode 100644 src/aoc2024/Day21.kt

diff --git a/src/aoc2024/Day21.kt b/src/aoc2024/Day21.kt
new file mode 100644
index 0000000..58f8a2d
--- /dev/null
+++ b/src/aoc2024/Day21.kt
@@ -0,0 +1,141 @@
+package aoc2024
+
+import RelPos
+import println
+import readInput
+
+/*
+--- Day 21: Keypad Conundrum ---
+https://adventofcode.com/2024/day/21
+*/
+fun main() {
+
+    val inlineTestInput = """
+029A
+980A
+179A
+456A
+379A
+"""
+
+    val doorPadMap = hashMapOf(
+        '7' to RelPos(-2, -3),
+        '8' to RelPos(-1, -3),
+        '9' to RelPos(0, -3),
+        '4' to RelPos(-2, -2),
+        '5' to RelPos(-1, -2),
+        '6' to RelPos(0, -2),
+        '1' to RelPos(-2, -1),
+        '2' to RelPos(-1, -1),
+        '3' to RelPos(0, -1),
+        '0' to RelPos(-1, 0),
+        'A' to RelPos(0, 0),
+    )
+
+    val robotPadMap = hashMapOf(
+        '^' to RelPos(-1, 0),
+        'A' to RelPos(0, 0),
+        '<' to RelPos(-2, 1),
+        'v' to RelPos(-1, 1),
+        '>' to RelPos(0, 1),
+    )
+
+    data class PadState(
+        var pos: RelPos,
+        val padMap: Map<Char, RelPos>,
+        val child: PadState? = null,
+        val cache: MutableMap<Pair<RelPos, RelPos>, Long> = HashMap()
+    ) {
+        fun getMovement(c: Char): Long {
+            val targetPos = padMap[c]!!
+            return if (child == null) {
+                1
+            } else {
+                val movement = cache.getOrPut(pos to targetPos) {
+                    val child = child
+                    var sum = 0L
+                    if (pos.dr == 0 && targetPos.dc == -2) {
+                        while (targetPos.dr < pos.dr) {
+                            sum += child.getMovement('^')
+                            pos = pos.translate(0, -1)
+                        }
+                        while (targetPos.dr > pos.dr) {
+                            sum += child.getMovement('v')
+                            pos = pos.translate(0, 1)
+                        }
+                    }
+                    if (pos.dc == -2 && targetPos.dr == 0) {
+                        while (targetPos.dc > pos.dc) {
+                            sum += child.getMovement('>')
+                            pos = pos.translate(1, 0)
+                        }
+                    }
+                    while (targetPos.dc < pos.dc) {
+                        sum += child.getMovement('<')
+                        pos = pos.translate(-1, 0)
+                    }
+                    while (targetPos.dr > pos.dr) {
+                        sum += child.getMovement('v')
+                        pos = pos.translate(0, 1)
+                    }
+                    while (targetPos.dr < pos.dr) {
+                        sum += child.getMovement('^')
+                        pos = pos.translate(0, -1)
+                    }
+                    while (targetPos.dc > pos.dc) {
+                        sum += child.getMovement('>')
+                        pos = pos.translate(1, 0)
+                    }
+
+                    sum += child.getMovement('A')
+                    sum
+                }
+
+                pos = targetPos
+                movement
+            }
+        }
+    }
+
+    fun part1(input: List<String>): Long {
+        val home = RelPos(0, 0)
+        val myPad = PadState(home, robotPadMap)
+        val robotPad2 = PadState(home, robotPadMap, myPad)
+        val robotPad1 = PadState(home, robotPadMap, robotPad2)
+        val doorPad = PadState(home, doorPadMap, robotPad1)
+        var sum = 0L
+        for (seq in input) {
+            val seqVal = seq.take(3).toLong()
+            sum += seq.sumOf { doorPad.getMovement(it) } * seqVal
+        }
+        return sum
+    }
+
+    fun part2(input: List<String>): Long {
+        val home = RelPos(0, 0)
+        val myPad = PadState(home, robotPadMap)
+        var lastPad = myPad
+        Array(25) { PadState(home, robotPadMap, lastPad).also { lastPad = it } }
+        val doorPad = PadState(home, doorPadMap, lastPad)
+        var sum = 0L
+        for (seq in input) {
+            val seqVal = seq.take(3).toLong()
+            sum += seq.sumOf { doorPad.getMovement(it) } * seqVal
+        }
+        return sum
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2024/Day21_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 126384L)
+    //check(testInputPart2Result == 0)
+
+    val input = readInput("aoc2024/Day21")
+    part1(input).println()
+    part2(input).println()
+}