Best Time to Buy and Sell Stock系列

 1 class Solution {
 2 public:
 3     int maxProfit(vector<int>& prices) {
 4            if(prices.size() < 1)   //prices.size is unsigned int
 5                 return 0;
 6            int pro = 0;
 7            for(int i=0; i<prices.size()-1; i++)
 8            {
 9                if(prices[i+1] >prices[i])
10                       pro += prices[i+1]-prices[i];
11            }
12            return pro;
13     }
14 };

 1 class Solution {
 2 public:
 3     int maxProfit(vector<int>& prices) {
 4         int n = prices.size(); 
 5         if(n < 2) 
 6             return 0;
 7         vector<int> sells(n, 0);
 8         vector<int> buys(n, 0);
 9         int delay = 0;
10         sells[0] = 0;
11         buys[0] = -prices[0];
12         sells[1] =  prices[1]-prices[0];
13         buys[1] =  -prices[1];
14         int res = max(0, prices[1]-prices[0]);
15         for(int i=2; i<n; ++i)
16         {
17             delay = prices[i]-prices[i-1];
18             buys[i] = max(sells[i-2]-prices[i], buys[i-1]-delay);
19             sells[i] = max(buys[i-1]+prices[i], sells[i-1]+delay);
20             if(res <sells[i])
21                   res = sells[i];
22         }
23         return res;
24     }
25 };