LeetCode --- Best Time to Buy and Sell Stock II

 1 class Solution {  2 public:  3     int maxProfit(vector<int> &prices) {  4         unsigned int len = prices.size();  5         if (len == 0) return 0;  6         // ans: holds the total profit that has been earned

 7         int ans = 0;  8         for (int i = 0; i < len; ) {  9             // buy: holds price of the ith day where 10             // i is the maximum index satisfing 11             // prices[i-1] > prices[i] and prices[i] <= prices[i+1]

12             int buy = prices[i++]; 13             while (i < len && prices[i] < buy) { 14                 buy = prices[i++]; 15  } 16             if (i >= len) return ans; 17             // sell: holds price of the ith day where 18             // i is the maximum index satisfing 19             // prices[i-1] < prices[i] and prices[i] >= prices[i+1]

20             int sell = prices[i++]; 21             while (i < len && prices[i] > sell) { 22                 sell = prices[i++]; 23  } 24             ans += (sell - buy); 25  } 26         

27         return ans; 28  } 29 };