117. 填充每个节点的下一个右侧节点指针 II

思路：层次遍历二叉树+每层串联起来

"""
# Definition for a Node.
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
"""

class Solution:
    def connect(self, root: 'Node') -> 'Node':
        '''
        思路：层次遍历，在每一层用一个Node节点串起来
        '''
        if not root:
            return root
        q = [root]
        while q:
            demmy_node = Node() # 每层的虚拟头节点
            leng = len(q)
            for _ in range(leng):
                node = q.pop(0)
                demmy_node.next = node
                
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
                    
                demmy_node = node
        return root