python中如何遍历树

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def maxdepth(self, root):

        if root is None:

            return 0

        return max(self.maxdepth(root.left), self.maxdepth(root.right))+1

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def preorder(self, root):

        if root is None:

            return ''

        print root.val

        if root.lef:

            self.preorder(root.left)

        if root.right:

            self.preorder(root.right)

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def midorder(self, root):

        if root is None:

            return ''

        if root.lef:

            self.midorder(root.left)

        print root.val

        if root.right:

            self.midorder(root.right)

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def endorder(self, root):

        if root is None:

            return ''

        if root.lef:

            self.endorder(root.left)

        if root.right:

            self.endorder(root.right)

        print root.val

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

　　def graorder(self, root):

　　　　if root is None:

　　　　　　return ''

　　　　queue = [root]

　　　　while queue:

　　　　　　res = []

　　　　　　for item in queue:

　　　　　　　　print item.val,

　　　　　　　　if item.left:

　　　　　　　　　　res.append(item.left)

　　　　　　　　if item.right:

　　　　　　　　　　res.apppend(item.right)

　　　　　　queue = res

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def issame(self, root1, root2):

        if root1 is None and root2 is None:

            return True

        elif root1 and root2:

            return root1.val==root2.val and issame(root1.left, root2.left) and issame(root1.right, root2.right)

        else:

            return False