Cruce primero en amplitud y recorrido jerárquico del árbol de Python

Cruce de nivel ;

class TreeNode():
	def __init__(self,x):
		self.val = x
		self.left = None
		self.right = None
class Solution(object):
　　def graorder(self, root):
			if not root:
				return ''
			queue = [root]
			res = []
			while queue:
				x = queue.pop(0)
				res.append(x)
				if x.left:
					quence.append(x.left)
				if x.right:
					queue.append(x.right)
			return res