[leetCode]剑指 Offer 37. 序列化二叉树

递归

可以使用前序遍历将二叉树序列化为字符串，遇到null用字符串“null,”代替。
反序列化时将序列化的结果转化为String数组，每次读取一个字符串，如果是数字则按照前序遍历继续递归。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    private StringBuffer buffer = new StringBuffer();
    
    private int number;

    private int index = 0;


    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if(root == null){
            buffer.append("null,");
            return buffer.toString();
        }
        buffer.append(root.val+",");
        serialize(root.left);
        serialize(root.right);
        return buffer.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        String[] nodes = data.split(",");
        //System.out.print(data);
        return rdeserialize(nodes);
    }

    private TreeNode rdeserialize(String[] data){
        if(!readOne(data)){
            return null;
        }
        TreeNode root = new TreeNode(number);
        root.left = rdeserialize(data);
        root.right = rdeserialize(data);
        return root;
    }

    //每次读取一个字符
    private boolean readOne(String[] data){
        if(data[index].equals("null")){
            ++index;
            return false;
        }else{
            number = Integer.valueOf(data[index]);
            ++index;
            return true;
        }
    }

}

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