best-time-to-buy-and-sell-stock

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

//给定数组，找出最大差值。