AoC 2021 Day 13

day13.ts

type FoldInstruction = {
  axis: 'x' | 'y';
  value: number;
}

type Input = {
  points: Map<string, Point>;
  foldInstructions: FoldInstruction[];
}

type Point = [number, number];

const parseInput = (input: string): Input => {
  const [rawPoints, rawInstructions] = input.trim().split(/\n\n/g);
  const points: Map<string, Point> = new Map();

  rawPoints.split(/\n/).forEach((rp) => {
    const [x, y] = rp.split(',').map(Number);
    points.set(`${x},${y}`, [x, y]);
  })

  const foldInstructions: FoldInstruction[] = rawInstructions.split(/\n/g).map(t => t.replace(/fold along /g, '')).map((ri) => {
    const [axis, v] = ri.split('=');
    return {
      axis: axis as 'x' | 'y',
      value: Number(v),
    }
  });

  return {
    points,
    foldInstructions,
  }
}

const performFold = (points: Map<string, Point>, fold: FoldInstruction): Map<string, Point> => {
  Array.from(points.values()).forEach((point) => {
    const [x, y] = point;
    const coordVal = fold.axis === 'x' ? x : y;

    if (coordVal >= fold.value) {
      points.delete(`${x},${y}`);
      const newCoord = 2 * fold.value - coordVal;
      const pt = fold.axis === 'x' ? [newCoord, y] : [x, newCoord];
      points.set(pt.join(','), pt as Point);
    }
  })

  return points;
}

export const solveP1 = (input: string) => {
  const { points, foldInstructions } = parseInput(input);
  performFold(points, foldInstructions[0]);
  return points.size;
};

export const solveP2 = (input: string) => {
  const { points, foldInstructions } = parseInput(input);
  foldInstructions.forEach(inst => performFold(points, inst));
  render(points)
}

const render = (points: Map<string, Point>) => {
  const pts = Array.from(points.values());
  const width = Math.max(...pts.map(p => p[0])) + 1;
  const height = Math.max(...pts.map(p => p[1])) + 1;

  const row: string[] = Array(width).fill('.');
  const map: string[][] = Array(height).fill(null).map(() => [...row]);
 
  points.forEach(([x, y]) => map[y][x] = '#');

  map.forEach(row => console.log(row.join('.')));
}