121. 买卖股票的最佳时机

 1 class Solution 
 2 {
 3 public:
 4     int maxProfit(vector<int>& prices) 
 5     {
 6         if(prices.empty()) return 0;
 7         int n = prices.size();
 8         int buy = prices[0];
 9         int res = 0;
10         for(int i = 1;i < n;i ++)
11         {
12             res = max(res,prices[i] - buy);
13             if(buy > prices[i]) buy = prices[i];
14         }
15         return res;
16     }
17 };