853. Car Fleet

Version #2 HashMap

62.06 %
class Solution {
    public int carFleet(int target, int[] position, int[] speed) {
        if (position == null || position.length == 0 || speed == null || speed.length == 0 || position.length != speed.length) {
            return 0;
        }
        Map<Integer, Double> time = new HashMap<>();
        for (int i = 0; i < position.length; i++) {
            time.put(position[i], 1.0 * (target - position[i]) / speed[i]);
        }
        Arrays.sort(position);
        int fleet = 1;
        double currTime = time.get(position[position.length - 1]);
        double prevTime = currTime;
        for (int i = position.length - 2; i >= 0; i--) {
            currTime = time.get(position[i]);
            if (currTime > prevTime) {
                prevTime = currTime;
                fleet++;
            }
        }
        return fleet;
    }
}

Version #1 TreeMap
一刷
class Solution {
    public int carFleet(int target, int[] position, int[] speed) {
        TreeMap<Integer, Double> map = new TreeMap<>(Collections.reverseOrder());
        for (int i = 0; i < position.length; i++) {
            double time = (target - position[i]) / (double) speed[i];
            map.put(position[i], time);
        }
        int fleet = 0;
        double slowest = 0;
        // key -> position, value -> time
        for (double currTime : map.values()) {
            if (currTime > slowest) {
                fleet++;
                slowest = currTime;
            }
        }
        return fleet;
    }
}