LeetCode – Refresh – Best Time to Buy and Sell Stock iii

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<int> &prices) {
 4         if (prices.size() < 2) return 0;
 5         int len = prices.size(), rec = prices[0], result = 0;
 6         vector<int> 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 };