LeetCode 297. 二叉树的序列化与反序列化

1、题目

2、分析

序列化：直接使用前序遍历，遇到null的，用特殊字符代替。返回拼接后的字符串
反序列化：利用递归的方法，遇到特殊字符，结束递归返回null即可（反序列化就是构造二叉树，涉及到构造二叉树的话，首先考虑找到根节点）

3、代码

以下代码用StringBuilder代替String直接拼接，会省很多时间。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {
    String SPE = ",";
    String NULL = "#";
    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if(root == null) return NULL;
        String val = String.valueOf(root.val);
        String left = serialize(root.left);
        String right = serialize(root.right);
        String subStr = val + SPE + left + SPE + right;
        return subStr;
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        String[] nodes = data.split(SPE);
        LinkedList<String> nodeList = new LinkedList<String>();
        for(String s: nodes){
            nodeList.add(s);
        }
        return deserialize(nodeList);
    }

    private TreeNode deserialize(LinkedList<String> nodeList){
        if(nodeList.isEmpty()) return null; 
        String str = nodeList.removeFirst();
        if(str.equals(NULL)){
            return null;
        }
        TreeNode node = new TreeNode(Integer.valueOf(str).intValue());
        node.left = deserialize(nodeList);
        node.right = deserialize(nodeList);
        return node;
    }
}