maximize_stock.py

# The cost of a stock on each day is given in an array, find the max profit that you can make by buying and selling in those days. For example, if the given array is {100, 180, 260, 310, 40, 535, 695}, the maximum profit can earned by buying on day 0, selling on day 3. Again buy on day 4 and sell on day 6. If the given array of prices is sorted in decreasing order, then profit cannot be earned at all.

def sell(lowidx, highidx):
  print("time to sell -------")
  print("buy:", lowidx)
  print("sell:", highidx)

def stock(arr):
  low = None # keep track of lowest value
  lowidx = None # keep track of lowest day
  high = None
  highidx = None

  for idx, x in enumerate(arr[:-1]):
    if low is None: # first lowest stock
      low = arr[idx]
      lowidx = idx
      print("first low", low)
    elif arr[idx] < low: # new lowest stock
      low = arr[idx]
      lowidx = idx
      print("low",low)

    if high is None and arr[idx+1] > low: # find first high 
      high = arr[idx+1]
      highidx = idx+1
      print("first high", high)
    elif high is not None and arr[idx+1] > high : # new highest stock
      high = arr[idx+1]
      highidx = idx+1
      print("high:", high)

    if arr[idx + 1] < arr[idx] and high is not None: # let's sell mid week
      sell(lowidx, highidx)
      lowidx = None
      highidx = None

  sell(lowidx, highidx) # sell on final day

stock([100, 80, 180, 260, 310, 40, 535, 695])