Given an array $A[1..n]$ which represents a daily stock price of a particular stock. You are

allowed $4$ transactions, $2$ buys and $2$ sells. Each transaction can involve exactly one stock.

And only one transaction per day is allowed. Give an algorithm to find what is the maximum

profit one can make. For full credits, your algorithm must run in $O(n)($Note: Goldman Sachs

interview question$)$