让 TreeNode 和list、dict等 一样支持str() 和 eval()

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

def func1(self, v,l=None,r=None):
    self.val = v
    self.left = l
    self.right = r
def func2(self):
    return 'TreeNode('+str(self.val) + ',' + str(self.left) + ',' + str(self.right) + ')'
TreeNode.__init__ = func1
TreeNode.__str__ = func2

class Solution:
    def serialize(self, root):
        """Encodes a tree to a single string.

        :type root: TreeNode
        :rtype: str
        """
        return str(root)


    def deserialize(self, data):
        """Decodes your encoded data to tree.

        :type data: str
        :rtype: TreeNode
        """
        return eval(data)