Car Fleet Python Solution with Tests

lcpy gen -n 853   # by problem number
lcpy gen -s car_fleet   # by problem name

Input: target = 12, position = [10,8,0,5,3], speed = [2,4,1,1,3]
Output: 3
Explanation:
- The cars starting at 10 (speed 2) and 8 (speed 4) become a fleet, meeting each other at 12. The fleet forms at target.
- The car starting at 0 (speed 1) does not catch up to any other car, so it is a fleet by itself.
- The cars starting at 5 (speed 1) and 3 (speed 3) become a fleet, meeting each other at 6. The fleet moves at speed 1 until it reaches target.

Input: target = 10, position = [3], speed = [3]
Output: 1
Explanation: There is only one car, hence there is only one fleet.

Input: target = 100, position = [0,2,4], speed = [4,2,1]
Output: 1

class Solution:
    # Time: O(n log n)
    # Space: O(n)
    def car_fleet(self, target: int, position: list[int], speed: list[int]) -> int:
        # Sort cars by position descending (closest to target first).
        cars = sorted(zip(position, speed, strict=False), reverse=True)
        fleets = 0
        slowest_arrival = 0.0
        for pos, spd in cars:
            arrival = (target - pos) / spd
            # A car forms a new fleet only if it arrives strictly later than
            # the fleet ahead of it; otherwise it catches up and merges.
            if arrival > slowest_arrival:
                fleets += 1
                slowest_arrival = arrival
        return fleets