297. Serialize and Deserialize Binary Tree

利用preorder，多加点括号区分左右子树

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

class Codec:

    def serialize(self, root):
        """Encodes a tree to a single string.
        
        :type root: TreeNode
        :rtype: str
        """
        # preorder traversal with ()
        if root is None:
            return "()"
        left = self.serialize(root.left)
        right = self.serialize(root.right)
        return "("+str(root.val)+left+right+")"
        

    def deserialize(self, data):
        """Decodes your encoded data to tree.
        
        :type data: str
        :rtype: TreeNode
        """
        # strip ()
        data = data[1:-1]
        if data:
            data_index = 0 
            for i in range(len(data)):
                if data[i] == "(":
                    data_index = i
                    break
            root = TreeNode(data[:data_index])
            # find split point
            count = 0
            split_index = 0
            for i in range(data_index, len(data)):
                if data[i] == "(":
                    count += 1
                if data[i] == ")":
                    count -= 1
                if count == 0:
                    split_index = i
                    break
            root.left = self.deserialize(data[data_index:split_index+1])
            root.right = self.deserialize(data[split_index+1:])
            return root
        else:
            return None
        

# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.deserialize(codec.serialize(root))