lintcode,二叉树的序列化和反序列化

设计一个算法，并编写代码来序列化和反序列化二叉树。将树写入一个文件被称为“序列化”，读取文件后重建同样的二叉树被称为“反序列化”。
如何反序列化或序列化二叉树是没有限制的，你只需要确保可以将二叉树序列化为一个字符串，并且可以将字符串反序列化为原来的树结构。
样例
给出一个测试数据样例， 二叉树{3,9,20,#,#,15,7}，表示如下的树结构：
3
/ \
9 20
/ \
15 7
我们的数据是进行BFS遍历得到的。当你测试结果wrong answer时，你可以作为输入调试你的代码。
你可以采用其他的方法进行序列化和反序列化。

解题思路：序列化过程类似层次遍历，需要注意的是判断节点是否为空，以及字符串拼接的细节。反序列化过程，用index记录对第几个节点做操作，节点保存在arraylist里面，每次判断是否是操作左孩子，如果是右孩子就index++。
一刷ac

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */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) {        if(root == null) return "{}";        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();        queue.offer(root);        String res = "{";        while(!queue.isEmpty()){            int size = queue.size();            for(int i = 0; i < size; i++){                TreeNode tmp = queue.poll();                if(tmp == root) {                    res += String.valueOf(tmp.val);                    queue.offer(tmp.left);                    queue.offer(tmp.right);                }                else{                    if(tmp == null) res += ",#";                    else{                        res += ",";                        res += String.valueOf(tmp.val);                        queue.offer(tmp.left);                        queue.offer(tmp.right);                    }                }            }        }        res += "}";        return res;    }    /**     * 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.equals("{}")){            return null;        }        String[] strs = data.substring(1, data.length()-1).split(",");        TreeNode root = new TreeNode(Integer.parseInt(strs[0]));        ArrayList<TreeNode> al = new ArrayList<TreeNode>();        al.add(root);        boolean isLeft = true;        int index = 0;        for(int i = 1; i < strs.length; i++){            if(strs[i].equals("#")){                if(!isLeft) index++;                isLeft = !isLeft;            }else{                TreeNode node = al.get(index);                TreeNode tmp = new TreeNode(Integer.parseInt(strs[i]));                if(isLeft) node.left = tmp;                else node.right = tmp;                al.add(tmp);                if(!isLeft) index++;                isLeft = !isLeft;            }        }        return root;    }}