Data Structure:  Array
	retrieve by index: O(1)
	if(sorted)
		search (binary):  O(log(n))
	else
		search (linear):  O(n)
	retrieve head: O(1)
	retrieve tail: O(1)
	enumerate in order: O(n)
	insert:  O(n)
	insert at head: O(n)
	insert at tail: O(1) if we have space, O(n) otherwise
	if(sorted)
		delete by index:  O(n)
	else
		delete by index:  O(1) (just copy the last item into the hole)
	delete head:  same as above
	delete tail:  O(1) 

Data Structure:  Linked List
	retrieve by index:  O(n)
	search:   O(n)
	retrieve head:  O(1)
	retrieve tail:  O(1) if we have a tail pointer, O(n) otherwise
	enumerate in order:  O(n)
	insert:  O(n) to find the spot, O(1) for the actual insertion
	insert at head:  O(1)
	insert at tail:  O(1) if we have a tail pointer, O(n) otherwise
	delete by index: O(n) to find the spot, O(1) for the actual deletion
	delete head:  O(1)
	delete tail:  O(1) if the list is doubly-linked and we have a tail pointer, O(n) otherwise

Recur left pointer
Look at our data
Recur on right pointer

Data Structure:  Tree
	retrieve by index:  O(n log(n))  
	search:   O(log(n))
	retrieve head (first item in order):  O(log(n)) 
	retrieve root:  O(1)
	retrieve tail (last item in order):   O(log(n))
	enumerate in order:  O(n log(n))
	insert:   O(log(n))
	insert at head:  O(log(n))
	insert at tail:  O(log(n))
	delete by index:  O(n log(n))
	delete head:      O(log(n))
	delete tail:      O(log(n))