Untitled

const fs = require('fs');
const lines = fs.readFileSync('input.txt').toString().split("\n").filter(v => v).map(x => x.split(' -> ')).reduce((acc, [point, point2], idx) => {
  const [x1, y1] = point.split(',').map(Number);
  const [x2, y2] = point2.split(',').map(Number);

  acc.push({
    x1,
    y1,
    x2,
    y2,
  });

  return acc;
}, [])

const computeRes = (lines = [], filterFunction = () => true) => {
  const intersections = new Map();

  lines
    .filter(filterFunction)
    .forEach(({ x1, y1, x2, y2 }) => {
      let moveX;
      let moveY;

      if (x1 === x2) {
        moveX = 0;
      }

      if (x1 < x2) {
        moveX = 1;
      }

      if (x1 > x2) {
        moveX = -1;
      }

      if (y1 === y2) {
        moveY = 0;
      }

      if (y1 < y2) {
        moveY = 1;
      }

      if (y1 > y2) {
        moveY = -1;
      }

      do {
        const pointValue = intersections.get(`${x1},${y1}`) || 0;

        intersections.set(`${x1},${y1}`, pointValue + 1);

        x1 += moveX;
        y1 += moveY;

      } while (x1 !== x2 + moveX || y1 !== y2 + moveY);
    })

  let intersectionsAboveTwo = 0;

  for (let [_, value] of intersections) {
    if (value >= 2) {
      intersectionsAboveTwo++;
    }
  }

  return intersectionsAboveTwo;
}

//a
console.log(computeRes(lines, ({ x1, x2, y1, y2 }) => (x1 === x2 || y1 === y2)));
//b
console.log(computeRes(lines));