class Solution(object):
 def connect(self, root):
 if not root:
 return 
 queue = [root]
 while queue:
 curr = queue.pop(0)
 if curr.left and curr.right:
 curr.left.next = curr.right
 if curr.next:
 curr.right.next = curr.next.left
 queue.append(curr.left)
 queue.append(curr.right)