题目：

题解：

class Solution:def connect(self, root: 'Node') -> 'Node':if not root:return root# 从根节点开始leftmost = rootwhile leftmost.left:# 遍历这一层节点组织成的链表，为下一层的节点更新 next 指针head = leftmostwhile head:# CONNECTION 1head.left.next = head.right# CONNECTION 2if head.next:head.right.next = head.next.left# 指针向后移动head = head.next# 去下一层的最左的节点leftmost = leftmost.leftreturn root