return root
que = deque()
que.append(root)
while que:
lvl_size = len(que)
prev = None
for _ in range(lvl_size):
curr = que.popleft()
if prev:
prev.next = curr
if curr.left:
que.append(curr.left)
if curr.right:
que.append(curr.right)
prev = curr
prev.next = TreeNode(-1)
if __name__ == '__main__':
root = TreeNode(12)
root.left = TreeNode(7)
root.right = TreeNode(1)
root.left.left = TreeNode(9)
root.right.left = TreeNode(10)
root.right.right = TreeNode(5)
connect_level_order_siblings(root)
print("Level order traversal using 'next' pointer: ")
root.print_level_order()
