day05.js

const fs = require("fs");

const segments = fs
  .readFileSync("day05.txt", { encoding: "utf-8" }) // read day??.txt content
  .replace(/\r/g, "") // remove all \r characters to avoid issues on Windows
  .split("\n") // Split on newline
  .filter(Boolean) // Remove empty lines
  .map((line) => {
    const [from, to] = line.split(" -> ").map((point) => {
      const [x, y] = point.split(",").map(Number);
      return { x, y };
    });
    return {
      from,
      to,
    };
  });

function part1() {
  const filteredSegments = segments.filter(
    (s) => s.from.x === s.to.x || s.from.y === s.to.y
  );
  let count = 0;
  const memory = new Map();
  function addPoint(key) {
    let content = memory.get(key);
    if (!content) {
      content = 0;
    }
    content++;
    if (content === 2) {
      count++;
    }
    memory.set(key, content);
  }
  for (const segment of filteredSegments) {
    // go from start to end
    const isHorizontal = segment.from.y === segment.to.y;
    let currentPoint = { x: segment.from.x, y: segment.from.y }; // {...segment.from}

    // for each point in the segment, add it to memory
    while (currentPoint.x !== segment.to.x || currentPoint.y !== segment.to.y) {
      addPoint([currentPoint.x, currentPoint.y].join(`,`));

      if (isHorizontal) {
        currentPoint.x += currentPoint.x < segment.to.x ? 1 : -1;
      } else {
        currentPoint.y += currentPoint.y < segment.to.y ? 1 : -1;
      }
    }
    addPoint([currentPoint.x, currentPoint.y].join(`,`));
  }

  console.log(count);
}

part1();

function part2() {
  let count = 0;
  const memory = new Map();
  function addPoint(key) {
    let content = memory.get(key);
    if (!content) {
      content = 0;
    }
    content++;
    if (content === 2) {
      count++;
    }
    memory.set(key, content);
  }
  for (const segment of segments) {
    // go from start to end
    const isHorizontal = segment.from.y === segment.to.y;
    const isVertical = segment.from.x === segment.to.x;
    let currentPoint = { x: segment.from.x, y: segment.from.y }; // {...segment.from}

    // for each point in the segment, add it to memory
    while (currentPoint.x !== segment.to.x || currentPoint.y !== segment.to.y) {
      addPoint([currentPoint.x, currentPoint.y].join(`,`));

      if (isHorizontal) {
        currentPoint.x += currentPoint.x < segment.to.x ? 1 : -1;
      } else if (isVertical) {
        currentPoint.y += currentPoint.y < segment.to.y ? 1 : -1;
      } else {
        currentPoint.x += currentPoint.x < segment.to.x ? 1 : -1;
        currentPoint.y += currentPoint.y < segment.to.y ? 1 : -1;
      }
    }
    addPoint([currentPoint.x, currentPoint.y].join(`,`));
  }

  console.log(count);
}

part2();