动态优化买股票

int maxProfit(vector<int>& prices) {
        if (prices.size() == 0)
        {
            return 0;
        }
        int min = prices[0]; 
        int result = 0;
        for (int i = 1; i < prices.size(); ++i)
        {
            if (result < prices[i] - min)
            {
                result = prices[i] - min;
            }
            if (prices[i] < min)
            {
                min = prices[i];
            }
        }
        return result;
    }

int maxProfit(vector<int>& prices) {
        int tmp,start=prices[0],retmax = 0;
        for(int i=1;i<prices.size();++i)
        {
            if(prices[i]>prices[i-1]){
                tmp =  prices[i] - start ;
            }else{
                start = prices[i]>start?start:prices[i];
            }
            retmax = tmp>retmax?tmp:retmax;
        }
        return retmax;
    }