## 題解 ```python= """ # 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': queue = [root] while queue: n = len(queue) for i in range(n): node = queue.pop(0) if node: next_node_index = i + 1 if next_node_index < n: node.next = queue[0] else: node.next = None if node.left: queue.append(node.left) if node.right: queue.append(node.right) return root ```