From a61a88b4448fa192d98b3d939d6024b7fdc3d1b6 Mon Sep 17 00:00:00 2001
From: Sander in 't Hout <sander@inthout.me>
Date: Sat, 14 Dec 2024 02:07:09 +0100
Subject: [PATCH] Add AoC 2024 day 13 solver

---
 assets/advent_of_code/2024_13_sample.txt      | 15 +++++
 .../advent_of_code/2024/_all_solvers.dart     |  1 +
 .../advent_of_code/2024/day_13_solver.dart    | 58 +++++++++++++++++++
 3 files changed, 74 insertions(+)
 create mode 100644 assets/advent_of_code/2024_13_sample.txt
 create mode 100644 lib/solvers/advent_of_code/2024/day_13_solver.dart

diff --git a/assets/advent_of_code/2024_13_sample.txt b/assets/advent_of_code/2024_13_sample.txt
new file mode 100644
index 0000000..444a287
--- /dev/null
+++ b/assets/advent_of_code/2024_13_sample.txt
@@ -0,0 +1,15 @@
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279
\ No newline at end of file
diff --git a/lib/solvers/advent_of_code/2024/_all_solvers.dart b/lib/solvers/advent_of_code/2024/_all_solvers.dart
index 0b9230f..addcf7b 100644
--- a/lib/solvers/advent_of_code/2024/_all_solvers.dart
+++ b/lib/solvers/advent_of_code/2024/_all_solvers.dart
@@ -6,3 +6,4 @@ export 'day_05_solver.dart';
 export 'day_06_solver.dart';
 export 'day_11_solver.dart';
 export 'day_12_solver.dart';
+export 'day_13_solver.dart';
diff --git a/lib/solvers/advent_of_code/2024/day_13_solver.dart b/lib/solvers/advent_of_code/2024/day_13_solver.dart
new file mode 100644
index 0000000..ce71d23
--- /dev/null
+++ b/lib/solvers/advent_of_code/2024/day_13_solver.dart
@@ -0,0 +1,58 @@
+import 'package:h3x_devtools/solvers/advent_of_code/2024/aoc_2024_solver.dart';
+
+typedef _ClawMachineAnalysis = ({int buttonAX, int buttonAY, int buttonBX, int buttonBY, int priceX, int priceY});
+
+class Day13Solver extends AdventOfCode2024Solver {
+
+  @override
+  final int dayNumber = 13;
+
+  @override
+  String getSolution(String input) {
+    String splitString = input.contains('\r\n\r\n') ? '\r\n\r\n' : input.contains('\r\r') ? '\r\r' : '\n\n';
+    List<_ClawMachineAnalysis> clawMachineAnalysis = input.split(splitString).map((lineSet) {
+      List<List<String?>> matches = RegExp(r'X\+(\d*), Y\+(\d*)|X=(\d*), Y=(\d*)').allMatches(lineSet).map((e) => e.groups([0, 1, 2, 3, 4])).toList();
+      return (buttonAX: int.parse(matches[0][1]!), buttonAY: int.parse(matches[0][2]!), buttonBX: int.parse(matches[1][1]!), buttonBY: int.parse(matches[1][2]!), priceX: int.parse(matches[2][3]!), priceY: int.parse(matches[2][4]!));
+    }).toList();
+
+    // Part 1
+    int usedTokensPart1 = 0;
+    for (({int buttonAX, int buttonAY, int buttonBX, int buttonBY, int priceX, int priceY}) analysis in clawMachineAnalysis) {
+      usedTokensPart1 += _getUsedTokens(analysis, false) ?? 0;
+    }
+
+    // Part 2
+    int usedTokensPart2 = 0;
+    for (({int buttonAX, int buttonAY, int buttonBX, int buttonBY, int priceX, int priceY}) analysis in clawMachineAnalysis) {
+      usedTokensPart2 += _getUsedTokens(analysis, true) ?? 0;
+    }
+
+    return 'Fewest tokens: $usedTokensPart1, fewest tokens correct: $usedTokensPart2';
+  }
+
+}
+
+int? _getUsedTokens(_ClawMachineAnalysis analysis, bool part2) {
+  double a1 = analysis.buttonAX.toDouble(), b1 = analysis.buttonBX.toDouble(), equals1 = analysis.priceX.toDouble() + (part2 ? 10000000000000 : 0);
+  double a2 = analysis.buttonAY.toDouble(), b2 = analysis.buttonBY.toDouble(), equals2 = analysis.priceY.toDouble() + (part2 ? 10000000000000 : 0);
+
+  // Use method of elimination
+  double elimFactor = -a1 / a2;
+  double b2Elim = b2 * elimFactor;
+  double equalsElim = equals2 * elimFactor;
+
+  double bAfterElim = b1 + b2Elim;
+  double equalsAfterElim = equals1 + equalsElim;
+
+  double bButtonPresses = equalsAfterElim / bAfterElim;
+  double aButtonPresses = (equals1 - b1 * bButtonPresses) / a1;
+
+  const double epsilon = 0.001;
+  if ((aButtonPresses - aButtonPresses.round()).abs() <= epsilon &&
+      (bButtonPresses - bButtonPresses.round()).abs() <= epsilon) {
+    // Valid result
+    return aButtonPresses.round() * 3 + bButtonPresses.round();
+  }
+
+  return null;
+}