景岁的Leetcode解题报告：297. Serialize and Deserialize Binary Tree(Python)

一种基于前序遍历的解法。

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

# 本解法是基于层次遍历的。序列化和反序列化中的队列中都会有None，但是循环时读到None时不会读它的左右节点。另外可以参考水中的鱼的前序遍历解法：
# http://fisherlei.blogspot.jp/2013/03/interview-serialize-and-de-serialize.html
class Codec:
    def serialize(self, root):
        """Encodes a tree to a single string.

        :type root: TreeNode
        :rtype: str
        """
        if root is None:
            return ''

        list = []
        list.append(root)
        i = 0
        # 优化的层次遍历，不使用Queue，直接使用一个list存储和遍历。
        while i < len(list):
            if list[i] is not None:
                list.append(list[i].left)
                list.append(list[i].right)
            i += 1

        # 将list打印成逗号分隔的字符串
        res_str = ''
        for j in range(len(list)):
            if list[j] is not None:
                res_str += str(list[j].val) + ','
            else:
                res_str += 'x' + ','

        return res_str[0:-1]

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

        :type data: str
        :rtype: TreeNode
        """
        if data == '':
            return None

        input = data.split(',')

        root = TreeNode(input[0])
        q = Queue.Queue(-1)
        q.put(root)
        i = 0
        # 逻辑是使用队列循环节点，然后有一个计数器，如果节点不是'x'，则计数器加2
        while q.qsize() > 0 and i + 2 < len(input):
            node = q.get()
            if node.val != 'x':
                i += 1
                left = TreeNode(input[i])
                if left.val != 'x':
                    node.left = left
                    q.put(left)
                i += 1
                right = TreeNode(input[i])
                if right.val != 'x':
                    right = TreeNode(input[i])
                    node.right = right
                q.put(right)

        return root


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