AoC/2024/12/index.ts

const fs = require('fs');

const input = fs.readFileSync(__dirname + '/input.txt', 'utf8');

interface Coord { x: number, y: number };
interface Plot { x: number, y: number, edges: number, corners: number };

const plots: Array<Array<string>> = input.split("\n").slice(0, -1).map((row: string) => row.split(''));

const height = plots.length;
const width = plots[0].length;

const regions: Array<Array<Plot>> = [];

function getAllAdjacentPlots({ x, y }: Coord) {
    const letter = plots[y][x];
    plots[y][x] = '.'+letter;

    const plot = { x, y, edges: 0, corners: 0 };

    let adj: Array<Plot> = [plot];

    let firstOneWasAnEdge = false;
    let lastOneWasAnEdge = false;
    [
        { x, y: y - 1 },
        { x: x + 1, y },
        { x, y: y + 1 },
        { x: x - 1, y },
    ].forEach((adjCoord, i) => {
        const adjLetter = plots[adjCoord.y]
            && plots[adjCoord.y][adjCoord.x]
            && plots[adjCoord.y][adjCoord.x];
        if (adjLetter === letter) {
            adj = [...adj, ...getAllAdjacentPlots(adjCoord)];
            lastOneWasAnEdge = false;
        } else if (adjLetter !== '.'+letter) {
            plot.edges++;
            if (lastOneWasAnEdge) {
                plot.corners++;
            }
            lastOneWasAnEdge = true;
        }
        if (i === 0) {
            firstOneWasAnEdge = lastOneWasAnEdge;
        }
    });
    if (firstOneWasAnEdge && lastOneWasAnEdge) {
        plot.corners++;
    }
    return adj;
}

for (let y = 0; y < plots.length; y++) {
    const row = plots[y];
    for (let x = 0; x < row.length; x++) {
        const char = row[x];
        if (char.startsWith('.')) {
            continue;
        }

        regions.push(getAllAdjacentPlots({ x, y }));
    }
}

console.log(regions);
let sum = 0;

regions.forEach((plots) => {
    const perim = plots.reduce((carry, { edges }) => carry + edges, 0);
    const vertices = plots.reduce((carry, { corners }) => carry + corners, 0);
    const area = plots.length;
    // Part 1
    // sum += perim * area;
    // Part 2
    sum += vertices * area;
});

console.log(sum);