python实现二叉树先序中序后续遍历

class Solution:
    def threeOrders(self , root):
        # write code here
        self.results=[[],[],[]]
        self.preorder(root)
        self.inorder(root)
        self.postorder(root)
        return self.results
    # 前序遍历
    def preorder(self,root):
        if root is None:
            return 
        self.results[0].append(root.val)
        self.preorder(root.left)
        self.preorder(root.right)
        # 中序遍历
    def inorder(self,root):
        if root is None:
            return 
        self.inorder(root.left)
        self.results[1].append(root.val)
        self.inorder(root.right)
        # 后序遍历
    def postorder(self,root):
        if root is None:
            return 
        self.postorder(root.left)
        self.postorder(root.right)
        self.results[2].append(root.val)