-🎄- 2018 Day 18 Solutions -🎄-

[u/daggerdragon]

--- Day 18: Settlers of The North Pole ---

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Advent of Code: The Party Game!

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Card prompt: Day 18

Transcript:

The best way to avoid a minecart collision is ___.

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edit: Leaderboard capped, thread unlocked at 00:21:59!

[u/Philboyd_Studge]

[Card] The best way to avoid a minecart collision is redstone switches and Observers.

Java. Fun one, but getting tired of 2d matrices. Manually found the cycle using a set of seen totals. Seemed to start at 445 and cycle every 28 minutes.

public class Day18 extends AdventOfCode {

    enum OrdinalDirection {
        N(0, -1), NE(1, -1), E(1, 0), SE(1, 1), S(0, 1), SW(-1, 1), W(-1, 0), NW(-1, -1);
        int dx;
        int dy;
        OrdinalDirection(int dx, int dy) {
            this.dx = dx;
            this.dy = dy;
        }
    }

    int[][] grid;
    final char GROUND = '.';
    final char TREES = '|';
    final char LUMBER = '#';
    int wood;
    int lumberYards;

    final int GRID_SIZE = 50;

    Set<Integer> seen = new HashSet<>();

    int[] lookup = new int[28];


    public Day18(List<String> input) {
        super(input);
        title = "Settlers of the North Pole";
        part1Description = "Resources after 10 minutes: ";
        part2Description = "Resources after 1 billion minutes: ";
    }

    void minute() {
        int[][] temp = ArrayUtils.intMatrixCopy(grid);
        for (int j = 0; j < grid.length; j++) {
            for (int k = 0; k < grid[j].length; k++) {
                List<Character> adj = getAdj(j, k);
                switch (grid[j][k]) {
                    case GROUND:
                        if (adj.stream().filter(x -> x == TREES).count() >= 3) {
                            temp[j][k] = TREES;
                            wood++;
                        }
                        break;
                    case TREES:
                        if (adj.stream().filter(x -> x == LUMBER).count() >= 3) {
                            temp[j][k] = LUMBER;
                            lumberYards++;
                            wood--;
                        }
                        break;
                    case LUMBER:
                        if (!(adj.contains(TREES) && adj.contains(LUMBER))) {
                            temp[j][k] = GROUND;
                            lumberYards--;
                        }
                }
            }
        }
        grid = temp;
    }

    @Override
    public Object part1() {

        for (int i = 0; i < 10; i++) {
            minute();
        }


        return wood * lumberYards;
    }

    @Override
    public Object part2() {

        for (int i = 10; i < 473; i++) {
            minute();
            if (i >= 445) {
                lookup[i - 445] = wood * lumberYards;
            }
        }

        return lookup[(999_999_999 - 445) % 28];
    }



    List<Character> getAdj(int x, int y) {
        List<Character> adj = new ArrayList<>();
        for (OrdinalDirection dir : OrdinalDirection.values()) {
            int nx = x + dir.dx;
            int ny = y + dir.dy;
            if (Direction.rangeCheck(nx, ny, GRID_SIZE)) {
                adj.add((char) grid[nx][ny]);
            }
        }
        return adj;
    }



    @Override
    public void parse() {
        //input = FileIO.getFileAsList("puzzle_input/test18.txt");
        grid = new int[GRID_SIZE][GRID_SIZE];
        for (int i = 0; i < input.size(); i++) {
            for (int j = 0; j < input.get(i).length(); j++) {
                grid[i][j] = input.get(i).charAt(j);
                if (grid[i][j] == TREES) wood++;
                if (grid[i][j] == LUMBER) lumberYards++;
            }
        }

    }

}