How to find the sum of nodes in a tree without recursion - python-3.x

Question

I've tried to solve this problem a few different ways.
The Node for my code is defined as:
A Node is an object
- value : Number
- children : List of Nodes
class Node:
def __init__(self, key, childnodes):
self.key = key
self.childnodes = childnodes
def __repr__(self):
return f'Node({self.key!r}, {self.childnodes!r})'
testTree = Node(1, [Node(2, []), Node(3, [Node(4, [Node(5, []), Node(6, [Node(7, [])])])])])
I've gotten close to completing the problem with the code:
def sum_of_nodes(root):
sum = 0
while root:
sum += root.key
print(sum)
root = root.childnodes
print(root)
root = root.pop()
print(root)
print(sum)
However, it skips some portions of the code and I'm not sure how to go about fixing it. The result of the above code is:
1
[Node(2, []), Node(3, [Node(4, [Node(5, []), Node(6, [Node(7, [])])])])]
Node(3, [Node(4, [Node(5, []), Node(6, [Node(7, [])])])])
4
[Node(4, [Node(5, []), Node(6, [Node(7, [])])])]
Node(4, [Node(5, []), Node(6, [Node(7, [])])])
8
[Node(5, []), Node(6, [Node(7, [])])]
Node(6, [Node(7, [])])
14
[Node(7, [])]
Node(7, [])
21
[]
Along with an error:
Traceback (most recent call last):
File "D:/Documents/project1.py", line 191, in <module>
print(f'itersum_of_nodes(testTree) => {itersum_of_nodes(testTree)}') # 28
File "D:/Documents/project1.py", line 108, in sum_of_nodes
root = root.pop()
IndexError: pop from empty list
I've also tried the method taught at geeksforgeeks.org/inorder-tree-traversal-without-recursion/ however, my children nodes are defined as a list rather than .right or .left and I'm not sure how to get the info I need out of it because of that. The code is:
stack = []
sum = 0
current = root
while True:
if current.childnodes[0] is not None:
stack.append(current)
current = current.childnodes[0]
elif stack:
current = stack.pop()
sum += current.value
current = current.childnodes[1]
else:
break

Answer 1

Here is a working version of while loop that traverses your tree without recursion. The main problem with this is that your nodes don't store the children individually, but rather as a list. This means that you need to be vigilant in checking how many children the node actually has.
def sum_of_nodes(root):
sum = 0
stack = []
# While the current node is not none
while root:
# Add the value of the current node to the sum
sum += root.key
# Check if the current node has children
if root.childnodes:
# If it has two children, append the second child to the stack
if len(root.childnodes) == 2:
stack.append(root.childnodes[1])
# Set the first child as the current node
root = root.childnodes[0]
# If the current node doesn't have any children, take one from the stack
elif stack:
root = stack.pop()
# If we run out of children in the stack, end the while loop
else:
break
return sum