1870-minimum-speed-to-arrive-on-time.js

/**
 * 1870. Minimum Speed to Arrive on Time
 * https://leetcode.com/problems/minimum-speed-to-arrive-on-time/
 * Difficulty: Medium
 *
 * You are given a floating-point number hour, representing the amount of time you have to reach
 * the office. To commute to the office, you must take n trains in sequential order. You are also
 * given an integer array dist of length n, where dist[i] describes the distance (in kilometers)
 * of the ith train ride.
 *
 * Each train can only depart at an integer hour, so you may need to wait in between each train
 * ride.
 * - For example, if the 1st train ride takes 1.5 hours, you must wait for an additional 0.5 hours
 *   before you can depart on the 2nd train ride at the 2 hour mark.
 *
 * Return the minimum positive integer speed (in kilometers per hour) that all the trains must
 * travel at for you to reach the office on time, or -1 if it is impossible to be on time.
 *
 * Tests are generated such that the answer will not exceed 107 and hour will have at most two
 * digits after the decimal point.
 */

/**
 * @param {number[]} dist
 * @param {number} hour
 * @return {number}
 */
var minSpeedOnTime = function(dist, hour) {
  const trainCount = dist.length;
  if (Math.ceil(trainCount - 1) > hour) return -1;

  let minSpeed = 1;
  let maxSpeed = 10000000;
  let result = -1;

  while (minSpeed <= maxSpeed) {
    const midSpeed = (minSpeed + maxSpeed) >> 1;
    let totalTime = 0;

    for (let i = 0; i < trainCount - 1; i++) {
      totalTime += Math.ceil(dist[i] / midSpeed);
    }
    totalTime += dist[trainCount - 1] / midSpeed;

    if (totalTime <= hour) {
      result = midSpeed;
      maxSpeed = midSpeed - 1;
    } else {
      minSpeed = midSpeed + 1;
    }
  }

  return result;
};