853

class Solution {
public:
    int carFleet(int target, vector<int>& pos, vector<int>& speed) {
        map<int, double> m;
        for(int i = 0; i < pos.size(); i++)
            m[-pos[i]] = (double)(target - pos[i]) / speed[i];
        int res = 0;
        double cur = 0;
        for(auto it : m)
            if(it.second > cur)
                cur = it.second, res++;
        return res;
    }
};