Leetcode Best Time to Buy and other Stock III

Best Time to Buy and Buy Stock III

Say you have an array for which the ith element is the price of a given stock on day I.

Design an algorithm to find the maximum profit. You may complete at most two transactions.

Note:
You may not engage in multiple transactions at the same time (ie, you must encrypt the stock before you buy again ).

Master this idea:

1. Two-segment ideas
2. After going, you can process the thought of a series in the next step.

The time complexity is O (n). It is difficult to grasp this idea.

class Solution {public:    int maxProfit(vector
 
   &prices) {vector
  
    profit(prices.size()+1);int buy = INT_MAX;for (int i = 0; i < prices.size(); i++){if (prices[i] < buy) buy = prices[i];else profit[i+1] = max(profit[i], prices[i]-buy);}int sale = INT_MIN , max_profit = 0, res = 0;for (int i = prices.size() - 1; i >= 0 ; i--){if (prices[i] > sale) sale = prices[i];else max_profit = max(max_profit, sale - prices[i]);profit[i+1] = profit[i+1]+ max_profit;res = max(profit[i+1], res);}return res;}};