day03.test.ts

/* === TYPES === */
enum Square {
  Open = "Open",
  Tree = "Tree",
}

type Slope = Square[][];

type Point = [number, number];

/* === PREPARE INPUT === */
const toSquare = (char: string): Square =>
  char === "#" ? Square.Tree : Square.Open;

const prepareInput = ([input]: TemplateStringsArray) =>
  input.split("\n").map((line) => [...line].map(toSquare)) as Slope;

/* === UTILS === */
const product = (numbers: number[]) =>
  numbers.reduce((acc, next) => acc * next, 1);

type GetSquareAt = (slope: Slope) => (point: Point) => Square;
const getSquareAt: GetSquareAt = (slope) => ([x, y]) =>
  slope[x][y % slope[0].length];

/* === IMPLEMENTATION === */
type CountTreesInPath = (slope: Slope, delta: Point) => number;
const countTreesInPath: CountTreesInPath = (slope, [dx, dy]) =>
  // Get number of moves until reaching the end
  [...Array((slope.length - 1) / dx + 1).keys()]
    // Repeat step to find point
    .map((i) => [dx * i, dy * i] as Point)
    .map(getSquareAt(slope))
    .filter((square) => square === Square.Tree).length;

/* === TESTS === */

test("Day 1a - test", () => {
  const slope = testInput;
  const trees = countTreesInPath(slope, [1, 3]);

  expect(trees).toBe(7);
});

test("Day 3a - prod", () => {
  const slope = prodInput;
  const trees = countTreesInPath(slope, [1, 3]);

  expect(trees).toBe(145);
});

test("Day 3b - test", () => {
  const slope = testInput;

  const deltas: Point[] = [
    [1, 1],
    [1, 3],
    [1, 5],
    [1, 7],
    [2, 1],
  ];

  const trees = deltas.map((delta) => countTreesInPath(slope, delta));

  expect(product(trees)).toBe(336);
});

test("Day 3b - prod", () => {
  const slope = prodInput;

  const deltas: Point[] = [
    [1, 1],
    [1, 3],
    [1, 5],
    [1, 7],
    [2, 1],
  ];

  const trees = deltas.map((delta) => countTreesInPath(slope, delta));

  expect(product(trees)).toBe(3424528800);
});

/* === INPUTS === */

const testInput = prepareInput`..##.......
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