Day13a: Solved

lib/day13.dart

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+// --- Day 13: Claw Contraption ---
+// https://adventofcode.com/2024/day/13
+
+import 'dart:math';
+
+import 'package:collection/collection.dart';
+
+final buttonRegExp = RegExp(r'X\+(\d+), Y\+(\d+)');
+final prizeRegExp = RegExp(r'X=(\d+), Y=(\d+)');
+
+const costAButton = 3;
+const costBButton = 1;
+
+int solveA(Iterable<String> input) {
+  var sum = 0;
+
+  for (final chunk in input
+      .where((line) => line.isNotEmpty)
+      .splitBefore((line) => line.startsWith('Button A:'))) {
+    final [ax, ay] = [
+      ...buttonRegExp
+          .firstMatch(chunk[0])!
+          .groups(const [1, 2]).map((s) => int.parse(s!))
+    ];
+    final [bx, by] = [
+      ...buttonRegExp
+          .firstMatch(chunk[1])!
+          .groups(const [1, 2]).map((s) => int.parse(s!))
+    ];
+    final [px, py] = [
+      ...prizeRegExp
+          .firstMatch(chunk[2])!
+          .groups(const [1, 2]).map((s) => int.parse(s!))
+    ];
+
+    var cost = 0;
+    for (var a = 1; a <= 100; a++) {
+      for (var b = 1; b <= 100; b++) {
+        if ((a * ax) + (b * bx) == px && (a * ay) + (b * by) == py) {
+          if (cost == 0) {
+            cost = (a * costAButton) + (b * costBButton);
+          } else {
+            cost = min(cost, (a * costAButton) + (b * costBButton));
+          }
+        }
+      }
+    }
+
+    sum += cost;
+  }
+
+  return sum;
+}

test/day13_test.dart

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+// --- Day 13: Claw Contraption ---
+// https://adventofcode.com/2024/day/13
+
+import 'dart:io';
+import 'package:advent_of_code_2024/day13.dart';
+import 'package:advent_of_code_2024/util.dart';
+import 'package:test/test.dart';
+
+final input = File('test/data/day13.txt').readAsLinesSync();
+
+void main() {
+  group('Part One', () {
+    test('Example 1', () {
+      expect(
+          solveA(r'''
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+'''
+              .asLines),
+          equals(280));
+    });
+    test('Example 2', () {
+      expect(
+          solveA(r'''
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+'''
+              .asLines),
+          equals(0));
+    });
+    test('Example 3', () {
+      expect(
+          solveA(r'''
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+'''
+              .asLines),
+          equals(200));
+    });
+    test('Example 4', () {
+      expect(
+          solveA(r'''
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279
+'''
+              .asLines),
+          equals(0));
+    });
+    test('Example 5', () {
+      expect(
+          solveA(r'''
+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
+'''
+              .asLines),
+          equals(480));
+    });
+    test('Solution', () {
+      expect(solveA(input), equals(36571));
+    });
+  });
+}