Print binary tree in BFS fashion with O(1) space

Question

I was wondering if it\'s possible to print a binary tree in breadth first order while using only O(1) space?

The difficult part is that one have to use additional sp

Answer 1

An interesting special case is heaps.

From heapq docs:

Heaps are binary trees for which every parent node has a value less than or equal to any of its children. This implementation uses arrays for which heap[k] <= heap[2*k+1] and heap[k] <= heap[2*k+2] for all k, counting elements from zero. For the sake of comparison, non-existing elements are considered to be infinite. The interesting property of a heap is that its smallest element is always the root, heap[0]. [explanation by François Pinard]

How a tree represented in memory (indexes of the array):

                               0

              1                                 2

      3               4                5               6

  7       8       9       10      11      12      13      14

15 16   17 18   19 20   21 22   23 24   25 26   27 28   29 30

In this case nodes in the array are already stored in a breadth first order.

for value in the_heap:
    print(value)

O(1) in space.