Advent of Code 2022 - Day 9

advent-of-code-2022-09.js

const KNOT_COUNT = 10;
const knots = new Array(KNOT_COUNT).fill().map((_) => ({ x: 0, y: 0 }));
const tailPositions = new Set();
tailPositions.add("0,0");

const moves = INPUT.split(/\n/).map((move) => {
  let [direction, distance] = move.split(" ");
  distance = +distance;
  return { direction, distance };
});
moves.forEach((move) => {
  for (let i = 0; i < move.distance; i++) {
    if (move.direction === "U") knots[0].y -= 1;
    if (move.direction === "D") knots[0].y += 1;
    if (move.direction === "L") knots[0].x -= 1;
    if (move.direction === "R") knots[0].x += 1;
    moveTail(0);
  }
});
console.log("Tail positions:", tailPositions.size);

function moveTail(headIdx) {
  const head = knots[headIdx];
  const tail = knots[headIdx + 1];
  const xDist = Math.abs(head.x - tail.x);
  const yDist = Math.abs(head.y - tail.y);
  if (xDist < 2 && yDist < 2) return;
  if (xDist === 2) {
    tail.x += head.x > tail.x ? 1 : -1;
    tail.y > head.y ? (tail.y -= 1) : tail.y === head.y ? 0 : (tail.y += 1);
  } else if (yDist === 2) {
    tail.y += head.y > tail.y ? 1 : -1;
    tail.x > head.x ? (tail.x -= 1) : tail.x === head.x ? 0 : (tail.x += 1);
  }
  if (headIdx === knots.length - 2) {
    tailPositions.add(`${tail.x},${tail.y}`);
  } else {
    moveTail(headIdx + 1);
  }
}