adventofcode/src/main/java/AoC2021_18.java at main · pareronia/adventofcode · GitHub

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import static java.util.stream.Collectors.toList;

import java.util.ArrayDeque;

import java.util.Deque;

import java.util.List;

import java.util.Objects;

import java.util.function.Supplier;

import java.util.stream.Stream;

import com.github.pareronia.aocd.Aocd;

import com.github.pareronia.aocd.Puzzle;

public class AoC2021_18 extends AoCBase {

private final List<String> inputs;

private AoC2021_18(final List<String> input, final boolean debug) {

super(debug);

this.inputs = input;

Reducer.debug = debug;

}

static final class Parser {

public static Number parse(final String line) {

final Deque<Number> stack = new ArrayDeque<>();

for (int i = 0; i < line.length(); i++) {

final Character ch = line.charAt(i);

if (ch == '[') {

continue;

} else if (Character.isDigit(ch)) {

stack.push(new Regular(Character.digit(ch, 10)));

} else if (ch == ',') {

continue;

} else {

final Number right = stack.pop();

final Number left = stack.pop();

final Pair pair = Pair.create(left, right);

stack.push(pair);

}

assert stack.size() == 1;

return stack.pop();

}

public static final AoC2021_18 create(final List<String> input) {

return new AoC2021_18(input, false);

}

public static final AoC2021_18 createDebug(final List<String> input) {

return new AoC2021_18(input, true);

}

static final class Exploder {

public static boolean explode(final Number number, final int depth) {

if (number instanceof Regular) {

return false;

}

final Pair pair = (Pair) number;

if (depth == 4) {

final Regular leftAdjacent = pair.leftAdjacent();

final Regular rightAdjacent = pair.rightAdjacent();

if (leftAdjacent != null) {

leftAdjacent.value += ((Regular) pair.left).getValue();

}

if (rightAdjacent != null) {

rightAdjacent.value += ((Regular) pair.right).getValue();

}

final Pair parent = (Pair) pair.parent;

assert parent != null;

if (Objects.equals(pair, parent.left)) {

parent.left = new Regular(0);

parent.left.parent = parent;

} else if (Objects.equals(pair, parent.right)) {

parent.right = new Regular(0);

parent.right.parent = parent;

} else {

throw new IllegalStateException();

}

return true;

}

return explode(pair.left, depth + 1) || explode(pair.right, depth + 1);

}

static final class Splitter {

public static boolean split(final Number number) {

return doSplit(number);

}

private static boolean doSplit(final Number number) {

if (number instanceof final Regular regular) {

final int value = regular.value;

if (value >= 10) {

final Pair pair = Pair.create(new Regular(value / 2), new Regular(value - value / 2));

pair.parent = regular.parent;

final Pair parent = (Pair) regular.parent;

if (regular.equals(parent.left)) {

parent.left = pair;

} else if (regular.equals(parent.right)) {

parent.right = pair;

} else {

throw new IllegalStateException();

}

return true;

} else {

return false;

}

final Pair pair = (Pair) number;

return doSplit(pair.left) || doSplit(pair.right);

}

static final class Reducer {

static boolean debug;

private static void log(final Supplier<Object> supplier) {

if (!debug) {

return;

}

System.out.println(supplier.get());

}

static void reduce(final Number number) {

log(() -> "Reducing: " + number);

while (true) {

if (Exploder.explode(number, 0)) {

log(() -> "after explode: " + number);

continue;

}

if (Splitter.split(number)) {

log(() -> "after split: " + number);

continue;

}

break;

}

static final class Adder {

public static Number add(final Number left, final Number right) {

return Pair.create(left, right);

}

static class Magnitude {

public static long magnitude(final Number number) {

if (number instanceof Regular) {

return ((Regular) number).value;

}

final Pair pair = (Pair) number;

return 3 * magnitude(pair.left) + 2 * magnitude(pair.right);

}

private Number solve(final List<Number> numbers) {

Number sum = numbers.get(0);

for (int i = 1; i< numbers.size(); i++) {

sum = Adder.add(sum, numbers.get(i));

Reducer.reduce(sum);

}

return sum;

}

private Number solve1() {

return solve(this.inputs.stream()

.map(Parser::parse)

.collect(toList()));

}

@Override

public Long solvePart1() {

final Number sum = solve1();

log("final sum is: " + sum);

return Magnitude.magnitude(sum);

}

@Override

public Long solvePart2() {

return this.inputs.stream()

.flatMap(s1 -> this.inputs.stream()

.filter(s2 -> !s2.equals(s1))

.flatMap(s2 -> {

final Number n1 = Parser.parse(s1);

final Number n2 = Parser.parse(s2);

return Stream.of(List.of(n1, n2));

}))

.map(this::solve)

.map(Magnitude::magnitude)

.mapToLong(Long::valueOf)

.max().orElseThrow();

}

public static void main(final String[] args) throws Exception {

assert AoC2021_18.create(List.of("[1,1]", "[2,2]", "[3,3]", "[4,4]", "[5,5]", "[6,6]")).solve1().toString().equals("[[[[5,0],[7,4]],[5,5]],[6,6]]");

assert AoC2021_18.create(TEST1).solve1().toString().equals("[[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]]");

assert AoC2021_18.create(TEST2).solvePart1() == 4_140L;

assert AoC2021_18.create(TEST2).solvePart2() == 3_993L;

final Puzzle puzzle = Aocd.puzzle(2021, 18);

puzzle.check(

() -> lap("Part 1", () -> AoC2021_18.create(puzzle.getInputData()).solvePart1()),

() -> lap("Part 2", () -> AoC2021_18.create(puzzle.getInputData()).solvePart2())

);

}

private static final List<String> TEST1 = splitLines(

"[[[0,[4,5]],[0,0]],[[[4,5],[2,6]],[9,5]]]\r\n" +

"[7,[[[3,7],[4,3]],[[6,3],[8,8]]]]\r\n" +

"[[2,[[0,8],[3,4]]],[[[6,7],1],[7,[1,6]]]]\r\n" +

"[[[[2,4],7],[6,[0,5]]],[[[6,8],[2,8]],[[2,1],[4,5]]]]\r\n" +

"[7,[5,[[3,8],[1,4]]]]\r\n" +

"[[2,[2,2]],[8,[8,1]]]\r\n" +

"[2,9]\r\n" +

"[1,[[[9,3],9],[[9,0],[0,7]]]]\r\n" +

"[[[5,[7,4]],7],1]\r\n" +

"[[[[4,2],2],6],[8,7]]"

);

private static final List<String> TEST2 = splitLines(

"[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]\r\n" +

"[[[5,[2,8]],4],[5,[[9,9],0]]]\r\n" +

"[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]\r\n" +

"[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]\r\n" +

"[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]\r\n" +

"[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]\r\n" +

"[[[[5,4],[7,7]],8],[[8,3],8]]\r\n" +

"[[9,3],[[9,9],[6,[4,9]]]]\r\n" +

"[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]\r\n" +

"[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]"

);

static abstract class Number {

protected Number parent = null;

}

static final class Regular extends Number {

private int value = -1;

public Regular(final int value) {

this.value = value;

}

public int getValue() {

return value;

}

@Override

public String toString() {

return String.valueOf(this.value);

}

static final class Pair extends Number {

private Number left = null;

private Number right = null;

public Pair(final Number left, final Number right) {

this.left = left;

this.right = right;

}

public static Pair create(final Number left, final Number right) {

final Pair pair = new Pair(left, right);

left.parent = pair;

right.parent = pair;

return pair;

}

public Number getLeft() {

return left;

}

public Number getRight() {

return right;

}

public Regular leftAdjacent() {

final Pair parent = getParent();

if (parent == null) {

return null;

}

if (this == parent.right) {

Number left = parent.left;

while (left instanceof Pair) {

left = ((Pair) left).right;

}

return (Regular) left;

}

return parent.leftAdjacent();

}

public Regular rightAdjacent() {

final Pair parent = getParent();

if (parent == null) {

return null;

}

if (this == parent.left) {

Number right = parent.right;

while (right instanceof Pair) {

right = ((Pair) right).left;

}

return (Regular) right;

}

return parent.rightAdjacent();

}

public Pair getParent() {

return (Pair) this.parent;

}

@Override

public String toString() {

return String.format("[%s,%s]", this.left, this.right);

}

adventofcode/src/main/java/AoC2021_18.java at main · pareronia/adventofcode · GitHub

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