import sys

lists = [[1,2,3],
         [-100, 70],
         [23, 50]]
pivot = [0] * len(lists) # [0, 0, 0]
finalSorted = []


for _ in range(sum(len(x) for x in lists)): # quantity of items in 2D array
	smallest = sys.maxint
  	index_of_smallest = -1
  	for indx, list in enumerate(lists):
  		if pivot[indx] < len(list):
  			current = list[pivot[indx]]
  		else:
  			continue
   		if current < smallest:
			smallest = current
			index_of_smallest = indx

  	finalSorted.append(smallest)
  	pivot[index_of_smallest] = pivot[index_of_smallest]+1

print(finalSorted) #[-100, 1, 2, 3, 23, 50, 70]