text: """116. Populating Next Right Pointers in Each Node
  https://leetcode.com/problems/populating-next-right-pointers-in-each-node/
  
  You are given a perfect binary tree where all leaves are on the same level,
  and every parent has two children.
  The binary tree has the following definition:
  
  Populate each next pointer to point to its next right node.
  If there is no next right node, the next pointer should be set to NULL.
  
  Initially, all next pointers are set to NULL.
  
  Follow up:
  
  You may only use constant extra space.
  Recursive approach is fine, you may assume implicit stack space does not
  count as extra space for this problem.
  
  Constraints:
  
  The number of nodes in the given tree is less than 4096.
  -1000 <= node.val <= 1000
  """
  from typing import List
  
  
  class Solution:
      def connect(self, root: 'Node') -> 'Node':
          def recur(node: Node) -> None:
              if not node:
                  return
              if node.left:
                  node.left.next = node.right
                  if node.next:
                      node.right.next = node.next.left
              recur(node.left)
              recur(node.right)
  
          recur(root)
          return root
  
  
  class Node:
      def __init__(self, val: int = 0, left: 'Node' = None, right: 'Node' = None,
                   next: 'Node' = None):
          self.val = val
          self.left = left
          self.right = right
          self.next = next
  