[Lintcode]Binary Tree Serialization

Design an algorithm and write code to serialize and deserialize a binary tree. Writing the tree to a file is called 'serialization' and reading back from the file to reconstruct the exact same binary tree is 'deserialization'.

There is no limit of how you deserialize or serialize a binary tree, you only need to make sure you can serialize a binary tree to a string and deserialize this string to the original structure.

Example

An example of testdata: Binary tree {3,9,20,#,#,15,7}, denote the following structure:

  3 / \9  20  /  \ 15   7

Our data serialization use bfs traversal. This is just for when you got wrong answer and want to debug the input.

You can use other method to do serializaiton and deserialization.

需要考虑的问题是1）用哪种方法遍历 前序/中序/后序/其他 2）如何表示空    难点是一般恢复二叉树至少需要两个序列，例如 前序+中序 或者中序+后序（前序+后序不能唯一确定一个二叉树）。

如果需要使用一个序列进行二叉树还原，则需使用Lintcode的二叉树表示法即层次遍历表示法来序列化。序列化时需要判断深度，深度未超过树深度的空节点用井号表示，否则不需要表示。

class Solution {        /**     * This method will be invoked first, you should design your own algorithm      * to serialize a binary tree which denote by a root node to a string which     * can be easily deserialized by your own "deserialize" method later.     */    public String serialize(TreeNode root) {        String res = "";        int depth = -1, curr = 1;                if(root == null) return res;        if(depth == -1) depth = getDepth(root);                LinkedList<TreeNode> list = new LinkedList<TreeNode>();        TreeNode dummy = new TreeNode(0);        list.add(root);        list.add(dummy);        res += String.valueOf(root.val) + ",";        while(list.size() != 1) {            TreeNode tmp = list.poll();            if(tmp.val == 0) {                curr += 1;                list.add(dummy);                continue;            }                        if(tmp.left != null) {list.add(tmp.left); res += tmp.left.val + ",";}            else {                if(curr + 1 <= depth) res += "#,";            }            if(tmp.right != null) {list.add(tmp.right); res += tmp.right.val + ",";}            else {                if(curr + 1 <= depth) res += "#,";            }        }        return res.substring(0, res.length() - 1);    }        int getDepth(TreeNode root){        if(root == null) return 0;        int res = 1;        return res + Math.max(getDepth(root.left), getDepth(root.right));    }        /**     * This method will be invoked second, the argument data is what exactly     * you serialized at method "serialize", that means the data is not given by     * system, it's given by your own serialize method. So the format of data is     * designed by yourself, and deserialize it here as you serialize it in      * "serialize" method.     */    public TreeNode deserialize(String data) {        if(data.length() == 0) return null;        LinkedList<TreeNode> list = new LinkedList<TreeNode>();         String[] dataList = data.split(",");        TreeNode res = null;                boolean left = true;        for(String str : dataList) {            if(str.equals("#")) {                TreeNode tmp = list.peek();                if(left){tmp.left = null; left = false;}                else {tmp.right = null; left = true; list.poll();}            } else {                TreeNode curr = new TreeNode(Integer.parseInt(str));                if(list.size() == 0) {list.add(curr); res = curr; continue;}                TreeNode tmp = list.peek();                if(left) {tmp.left = curr; left = false;}                else {tmp.right = curr; left = true; list.poll();}                list.add(curr);            }        }        return res;    }}