# 123 Best Time to Buy and Sell Stock III

input是一個array裡面存某股票每天的價格， 算出在兩次transaction內可以獲得的最高利潤。

• Idea:

  test case:
  [7,1,4,3,6,5,8]
  (1,4) -> 3
  (3,8) -> 5
  total -> 8
  
  keep four variables:
  firstBuy
  firstSell
  secondBuy
  secondSell
  
  if()