Tree traversal - preorder

tree_traversal_preorder_interative.py

def preorder_traversal_iterating(root):
    if not root:
        return []
    
    result = []
    # using stack
    stack = [root]
    while stack:
        current = stack.pop()
        # visit node
        result.append(current.val)
        # put right to stack first as we want to visit right after left!!
        if current.right:
            stack.append(current.right)
        if current.left:
            stack.append(current.left)
    return result