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Day 21
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‎src/test/java/com/macasaet/Day21.java

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package com.macasaet;
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import org.junit.jupiter.api.Test;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.stream.StreamSupport;
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/**
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* --- Day 21: Monkey Math ---
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* <a href="https://adventofcode.com/2022/day/21">https://adventofcode.com/2022/day/21</a>
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*/
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public class Day21 {
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public record Monkey(String name, Job job) {
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public long yell(final Map<String, Monkey> monkeys, final Map<String, Long> results) {
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return job().yell(monkeys, results);
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}
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public Simplification simplify(final Map<String, Monkey> monkeys, final Map<String, Long> results) {
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return job().simplify(monkeys, results);
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}
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public static Monkey parse(final String line) {
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final var components = line.split(": ");
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final var name = components[0].trim();
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final var job = Job.parse(components[1].trim());
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return new Monkey(name, job);
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}
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}
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public interface Simplification {
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Simplification simplify();
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}
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record Expression(Simplification x, Operation operation, Simplification y) implements Simplification {
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public Simplification simplify() {
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final var simpleX = x().simplify();
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final var simpleY = y().simplify();
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if (!x().equals(simpleX) || !y().equals(simpleY)) {
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return new Expression(simpleX, operation(), simpleY);
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} else if (x() instanceof Value && y() instanceof Value) {
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return new Value(operation().operate(((Value) x).value(), ((Value) y).value()));
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} else if (operation() == Operation.IS_EQUAL) {
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if (x() instanceof final Value constant && y() instanceof final Expression expression) {
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// e.g. 5=2/x or 5=x/2
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final var inverse = expression.operation().inverse();
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if (expression.x() instanceof Value) {
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// e.g. 5=2/x
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if (expression.operation.isSymmetric()) {
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// e.g. 2=5x -> 10=x
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final var lValue = new Expression(constant, inverse, expression.x()).simplify();
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return new Expression(lValue, Operation.IS_EQUAL, expression.y());
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} else {
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// e.g. 5=2/x -> 5x=2
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final var lValue = new Expression(constant, inverse, expression.y());
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return new Expression(lValue, Operation.IS_EQUAL, expression.x());
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}
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} else if (expression.y() instanceof Value) {
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// e.g. 5=x/2 -> 5*2=x -> 10=x
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final var lValue = new Expression(constant, inverse, expression.y()).simplify();
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return new Expression(lValue, Operation.IS_EQUAL, expression.x());
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}
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// cannot simplify further
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return this;
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} else if (x() instanceof final Expression expression && y() instanceof final Value constant) {
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// e.g. 5/x=2 or x/5=2
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final var inverse = expression.operation().inverse();
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if (expression.x() instanceof Value) {
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// e.g. 5/x=2 or x/5=2
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if (expression.operation().isSymmetric()) {
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// e.g. 2x=5 -> x=5*2 -> x=10
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final var rValue = new Expression(constant, inverse, expression.x()).simplify();
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return new Expression(expression.y(), Operation.IS_EQUAL, rValue);
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} else {
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// e.g. 5/x=2 -> 5=2x
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final var rValue = new Expression(constant, inverse, expression.y());
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return new Expression(expression.x(), Operation.IS_EQUAL, rValue);
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}
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} else if (expression.y() instanceof Value) {
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// e.g. x/5=2 -> x=2*5 -> x=10
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final var rValue = new Expression(constant, inverse, expression.y()).simplify();
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return new Expression(expression.x(), Operation.IS_EQUAL, rValue);
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}
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// cannot simplify further
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return this;
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}
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}
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return this;
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}
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public String toString() {
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return "(" + x() + ") " + operation() + " (" + y() + ")";
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}
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}
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record Value(long value) implements Simplification {
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public String toString() {
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return "" + value();
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}
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public Simplification simplify() {
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return this;
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}
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}
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record Variable() implements Simplification {
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public String toString() {
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return "x";
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}
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public Simplification simplify() {
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return this;
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}
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}
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public interface Job {
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long yell(final Map<String, Monkey> monkeys, final Map<String, Long> results);
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Simplification simplify(final Map<String, Monkey> monkeys, final Map<String, Long> results);
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static Job parse(final String string) {
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final var components = string.trim().split(" ");
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if (components.length == 1) {
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return Yell.parse(string.trim());
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}
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return Math.parse(components);
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}
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}
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public enum Operation {
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Add {
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public long operate(final long x, final long y) {
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return x + y;
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}
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public Operation inverse() {
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return Subtract;
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}
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public boolean isSymmetric() {
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return true;
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}
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},
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Subtract {
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public long operate(final long x, final long y) {
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return x - y;
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}
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public Operation inverse() {
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return Add;
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}
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public boolean isSymmetric() {
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return false;
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}
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},
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Multiply {
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public long operate(final long x, final long y) {
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return x * y;
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}
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public Operation inverse() {
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return Divide;
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}
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public boolean isSymmetric() {
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return true;
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}
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},
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Divide {
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public long operate(final long x, final long y) {
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return x / y;
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}
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public Operation inverse() {
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return Multiply;
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}
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public boolean isSymmetric() {
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return false;
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}
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},
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IS_EQUAL {
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public long operate(final long x, final long y) {
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// what a horrible hack, who would do this?
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return x == y ? 1L : 0L;
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}
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public Operation inverse() {
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return IS_EQUAL;
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}
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public boolean isSymmetric() {
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return true;
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}
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};
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public abstract long operate(long x, long y);
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public abstract Operation inverse();
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public abstract boolean isSymmetric();
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public String toString() {
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return switch (this) {
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case Add -> "+";
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case Subtract -> "-";
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case Multiply -> "*";
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case Divide -> "/";
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case IS_EQUAL -> "=";
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};
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}
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public static Operation parse(final String operator) {
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return switch (operator.trim()) {
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case "+" -> Add;
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case "-" -> Subtract;
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case "*" -> Multiply;
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case "/" -> Divide;
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default -> throw new IllegalArgumentException("Invalid operator: " + operator);
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};
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}
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}
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public record Unknown() implements Job {
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public long yell(Map<String, Monkey> monkeys, Map<String, Long> results) {
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throw new UnsupportedOperationException(); // Oof
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}
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public Simplification simplify(Map<String, Monkey> monkeys, Map<String, Long> results) {
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return new Variable();
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}
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}
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record Yell(long number) implements Job {
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public long yell(Map<String, Monkey> monkeys, Map<String, Long> results) {
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return number;
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}
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public Simplification simplify(Map<String, Monkey> monkeys, Map<String, Long> results) {
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return new Value(number());
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}
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public static Yell parse(final String string) {
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return new Yell(Integer.parseInt(string));
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}
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}
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public record Math(String monkeyX, Operation operation, String monkeyY) implements Job {
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public long yell(Map<String, Monkey> monkeys, Map<String, Long> results) {
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final var x = getVariable(monkeyX(), monkeys, results);
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final var y = getVariable(monkeyY(), monkeys, results);
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return operation().operate(x, y);
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}
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public Simplification simplify(Map<String, Monkey> monkeys, Map<String, Long> results) {
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final var x = monkeys.get(monkeyX()).simplify(monkeys, results);
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final var y = monkeys.get(monkeyY()).simplify(monkeys, results);
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if (x instanceof final Value xValue && y instanceof final Value yValue) {
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return new Value(operation().operate(xValue.value(), yValue.value()));
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}
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return new Expression(x, operation(), y);
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}
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long getVariable(final String monkeyName, final Map<String, Monkey> monkeys, final Map<String, Long> results) {
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if (results.containsKey(monkeyName)) {
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return results.get(monkeyName);
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}
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final var result = monkeys.get(monkeyName).yell(monkeys, results);
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results.put(monkeyName, result);
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return result;
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}
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public static Math parse(final String[] components) {
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final var monkeyX = components[0].trim();
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final var operation = Operation.parse(components[1].trim());
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final var monkeyY = components[2].trim();
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return new Math(monkeyX, operation, monkeyY);
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}
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}
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protected static Map<String, Monkey> getInput() {
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final Map<String, Monkey> result = new HashMap<>();
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StreamSupport.stream(new LineSpliterator("day-21.txt"), false)
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.map(Monkey::parse)
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.forEach(monkey -> result.put(monkey.name(), monkey));
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return Collections.unmodifiableMap(result);
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}
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@Test
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public final void part1() {
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final var monkeys = getInput();
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final var results = new HashMap<String, Long>();
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final var result = monkeys.get("root").yell(monkeys, results);
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System.out.println("Part 1: " + result);
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}
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@Test
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public final void part2() {
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final var monkeys = new HashMap<>(getInput());
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final var results = new HashMap<String, Long>();
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final var oldRoot = monkeys.get("root");
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final var oldJob = (Math) oldRoot.job();
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monkeys.put("root", new Monkey("root", new Math(oldJob.monkeyX(), Operation.IS_EQUAL, oldJob.monkeyY())));
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monkeys.put("humn", new Monkey("humn", new Unknown()));
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var simplification = monkeys.get("root").simplify(monkeys, results);
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while (true) {
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final var candidate = simplification.simplify();
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if (candidate.equals(simplification)) {
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break;
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}
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simplification = candidate;
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}
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System.out.println("Part 2: " + simplification);
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}
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}

‎src/test/resources/sample/day-21.txt

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root: pppw + sjmn
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dbpl: 5
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cczh: sllz + lgvd
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zczc: 2
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ptdq: humn - dvpt
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dvpt: 3
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lfqf: 4
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humn: 5
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ljgn: 2
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sjmn: drzm * dbpl
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sllz: 4
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pppw: cczh / lfqf
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lgvd: ljgn * ptdq
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drzm: hmdt - zczc
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hmdt: 32

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