Car Fleet II LeetCode solution in JavaScript

1
var getCollisionTimes = function (cars) {
2
  // create a stack to hold all the indicies of the cars that can be hit
3
  const possibleCarsToHit = [];
4
  const result = new Array(cars.length).fill(-1);
5

6
  for (let i = cars.length - 1; i >= 0; i--) {
7
    // if there are cars to hit, check if the current car will hit the car before or after hitting
8
    // the car in front of them
9
    // you can also think of this as if the current car will hit the car before or after being absorbed by
10
    // the slower car in front.
11
    while (
12
      possibleCarsToHit.length &&
13
      result[possibleCarsToHit[possibleCarsToHit.length - 1]] >= 0
14
    ) {
15
      const nextCarIndex = possibleCarsToHit[possibleCarsToHit.length - 1];
16
      const timeToCatchNextCar = getTimeToCatchNextCar(
17
        cars[i],
18
        cars[nextCarIndex]
19
      );
20
      const timeToCatchNextNextCar = result[nextCarIndex];
21
      if (
22
        timeToCatchNextCar > 0 &&
23
        timeToCatchNextCar <= timeToCatchNextNextCar
24
      ) {
25
        break;
26
      }
27

28
      // pop off the stack because the car was absorbed by the next car
29
      // before getting hit by the current car
30
      possibleCarsToHit.pop();
31
    }
32
    if (possibleCarsToHit.length) {
33
      const nextCarIndex = possibleCarsToHit[possibleCarsToHit.length - 1];
34
      result[i] = getTimeToCatchNextCar(cars[i], cars[nextCarIndex]);
35
    }
36
    possibleCarsToHit.push(i);
37
  }
38
  return result;
39
};
40

41
function getTimeToCatchNextCar(leftCar, rightCar) {
42
  const [leftCarPosition, leftCarSpeed] = leftCar;
43
  const [rightCarPosition, rightCarSpeed] = rightCar;
44
  const distanceToCatchCar = rightCarPosition - leftCarPosition;
45
  const differenceInSpeed = leftCarSpeed - rightCarSpeed;
46
  return differenceInSpeed > 0 ? distanceToCatchCar / differenceInSpeed : -1;
47
}