III is a kind of I. But it require 2 maximum value. So scan from begin and scan from end to record the maximum value for currrent index.

Then scan the maximum array to obtain the global maximum.

1 class Solution { 2 public: 3     int maxProfit(vector
     
       &prices) { 4         if (prices.size() < 2) return 0; 5         int len = prices.size(), rec = prices[0], result = 0; 6         vector
      
        left(len, 0), right(len, 0); 7         for (int i = 1; i < len; i++) { 8             left[i] = max(left[i-1], prices[i] - rec); 9             rec = min(rec, prices[i]);10         }11         rec = prices[len-1];12         for (int i = len-2; i >= 0; i--) {13             right[i] = max(right[i+1], rec - prices[i]);14             rec = max(prices[i], rec);15         }16         for (int i = 0; i < len; i++) {17             result = max(result, left[i] + right[i]);18         }19         return result;20     }21 };