best time to buy and sell stock ii

class  {
public:
    int maxProfit(vector<int> &prices) {
        if(prices.empty())
            return 0;
        vector<int> price_d(prices.size());
        for(int i = 0; i < prices.size()-1; i++)
        {
            price_d[i] = prices[i+1] - prices[i];
        }
        int max = 0;
        for(int i = 0; i < price_d.size(); i ++)
        {
            if(price_d[i] > 0)
                max += price_d[i];
        }
        return max;
    }
};