day-6/script.ts


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import fs from "fs";

const input = fs.readFileSync("./input.txt").toString();

const [times, distances] = input
  .split("\n")
  .slice(0, 2)
  .map((s) => s.match(/\d+/g)?.map(Number) || []);

function numberOfWaysToWin(time: number, record: number) {
  // Solution to quadratic:
  // x(time-x) > record
  // on the domain [0, time]
  const sqrt = Math.sqrt(time * time - 4 * record);
  const [min, max] = [-1, +1].map((sign) => 0.5 * (time + sqrt * sign));

  const wholeMin = Math.floor(min) + 1;
  const wholeMax = Math.ceil(max);
  return wholeMax - wholeMin;
}

const result = times
  .map((time, index) => {
    const distance = distances[index];
    return numberOfWaysToWin(time, distance);
  })
  .reduce((acc, v) => acc * v, 1);

console.log(result);