LeetCode 297 二叉樹的序列化和反序列化

這個題難度其實不大，

利用深度優先遍歷構建字符串，同時也利用深度遍歷返回樹。

class Codec:

    def __init__(self):
        self.idx = 0

    def serialize(self, root):
        """Encodes a tree to a single string.
        :type root: TreeNode
        :rtype: str
        """
        p = root
        stack, nodes = [], []
        while stack or p:
            if p:
                nodes.append(str(p.val))
                stack.append(p)
                p = p.left
            else:
                nodes.append('None')
                p = stack.pop()
                p = p.right
        nodes.append('None')
        return ' '.join(nodes)

    def deserialize(self, data):
        """Decodes your encoded data to tree.
        :type data: str
        :rtype: TreeNode
        """
        list1 = data.split(' ')
        self.idx = 0
        return self.constructTree(list1)

    def constructTree(self, list1):
        if self.idx >= len(list1) or list1[self.idx] == 'None':
            self.idx += 1
            return None
        val = int(list1[self.idx])
        self.idx += 1
        node = TreeNode(val)
        node.left = self.constructTree(list1)
        node.right = self.constructTree(list1)
        return node