LeetCode "Teemo Attacking"

Isn‘t it ‘Easy‘?

class Solution {
public:
    int findPoisonedDuration(vector<int>& ts, int d)
    {
        int ret = 0, s = 0, e = 0;
        for(auto t : ts)
        {
            if(t > e)
            {
                ret += e - s;
                s = t;
            }

            e = t + d;
        }
        ret += e - s;

        return ret;
    }
};