aoc 2024 day 13; call me a cheater, I don't care. I'm not writing a matrix LOL

Author: jacobsandersen

build.gradle.kts

@@ -13,6 +13,7 @@ dependencies {
  implementation("org.apache.commons:commons-text:1.12.0")
  implementation("org.apache.commons:commons-lang3:3.17.0")
  implementation("org.jgrapht:jgrapht-core:1.5.2")
+ implementation("org.ejml:ejml-simple:0.43.1")
  testImplementation(platform("org.junit:junit-bom:5.9.1"))
  testImplementation("org.junit.jupiter:junit-jupiter")
 }

src/main/java/dev/jacobandersen/codechallenges/challenge/adventofcode/year2024/day13/Day13.java

@@ -1,20 +1,103 @@
 package dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day13;
 
 import dev.jacobandersen.codechallenges.challenge.adventofcode.Day;
+import org.ejml.simple.SimpleMatrix;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 public class Day13 extends Day {
+ private final Pattern pattern = Pattern.compile("^.*[+=](\\d+).*[+=](\\d+)$");
+
  public Day13() {
  super(2024, 13, "Claw Contraption");
  }
 
+ record Machine(double[] x, double[] y) {
+ private long[] solve() throws RuntimeException {
+ final SimpleMatrix A = new SimpleMatrix(2, 2);
+ A.set(0, 0, x[0]);
+ A.set(0, 1, x[1]);
+ A.set(1, 0, y[0]);
+ A.set(1, 1, y[1]);
+
+ final SimpleMatrix B = new SimpleMatrix(2, 1);
+ B.set(0, 0, x[2]);
+ B.set(1, 0, y[2]);
+
+ final SimpleMatrix sol = A.solve(B);
+
+ long solA = Math.round(sol.get(0)), solB = Math.round(sol.get(1));
+
+ double xCheck = (x[0] * solA) + (x[1] * solB);
+ double yCheck = (y[0] * solA) + (y[1] * solB);
+
+ if (Math.abs(xCheck - x[2]) < 1e-6 && Math.abs(yCheck - y[2]) < 1e-6) {
+ return new long[] {solA, solB};
+ } else throw new RuntimeException("No integer solution.");
+ }
+
+ @Override
+ public String toString() {
+ return "Machine{" +
+ "x=" + Arrays.toString(x) +
+ ", y=" + Arrays.toString(y) +
+ '}';
+ }
+ }
+
+ private double[] matchLine(String line) {
+ Matcher matcher = pattern.matcher(line);
+ if(!matcher.matches()) throw new IllegalArgumentException();
+ return new double[]{Double.parseDouble(matcher.group(1)), Double.parseDouble(matcher.group(2))};
+ }
+
+ private List<Machine> loadMachines() {
+ List<String> lines = getInputLinesNoBlanks();
+
+ List<Machine> machines = new ArrayList<>();
+ for (int i = 0; i < lines.size(); i+=3) {
+ final double[] x = new double[3], y = new double[3];
+
+ final double[] a = matchLine(lines.get(i)), b = matchLine(lines.get(i+1)), prize = matchLine(lines.get(i+2));
+ x[0] = a[0];
+ y[0] = a[1];
+ x[1] = b[0];
+ y[1] = b[1];
+ x[2] = prize[0];
+ y[2] = prize[1];
+
+ machines.add(new Machine(x, y));
+ }
+
+ return machines;
+ }
+
+ private long countTokens(List<Machine> machines) {
+ return machines.stream().mapToLong(machine -> {
+ try {
+ final long[] solution = machine.solve();
+ return (3 * solution[0]) + solution[1];
+ } catch (RuntimeException ignored) {}
+
+ return 0;
+ }).sum();
+ }
+
  @Override
  public String partOne() {
- getInputLinesNoBlanks().forEach(System.out::println);
- return "";
+ return String.valueOf(countTokens(loadMachines()));
  }
 
  @Override
  public String partTwo() {
- return "";
+ return String.valueOf(countTokens(loadMachines().stream().map(m -> {
+ final double[] x = new double[] { m.x[0], m.x[1], m.x[2] + 10_000_000_000_000d };
+ final double[] y = new double[] { m.y[0], m.y[1], m.y[2] + 10_000_000_000_000d };
+ return new Machine(x, y);
+ }).toList()));
  }
 }