449. Serialize and Deserialize BST

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize a binary search tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.

The encoded string should be as compact as possible.

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

Serialization: preorder root -> left -> right;

Deserialize: preorder得到的序列 用dfs 先找root

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

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        StringBuilder sb  = new StringBuilder();
        serializeDFS(root, sb); //preorder root - left - right
        return sb.toString();
    }
    
    public void serializeDFS(TreeNode root, StringBuilder sb){
        if(root == null) return;
        sb.append(root.val).append(",");
        serializeDFS(root.left, sb);
        serializeDFS(root.right, sb);
    }
    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if(data == null || data.length() == 0) return null;
        String arr[] = data.split(",");
        return deserializeDFS(arr, 0, arr.length-1);
    }
    
    public TreeNode deserializeDFS(String[] array, int left, int right){
        if(left > right || left >= array.length) return null;
        TreeNode root = new TreeNode(Integer.parseInt(array[left]));
        int mid = getMid(array, left, right);
        root.left = deserializeDFS(array, left + 1, mid - 1);
        root.right = deserializeDFS(array, mid, right);
        return root;
    }
    
    public int getMid(String[] array, int left, int right){
        int index = 0;
        System.out.println(left);
        int init = Integer.parseInt(array[left]);
        while(left <= right){
            if(init < Integer.parseInt(array[left])) {
                break;
            }
            else left++;
        }
        return left;
    }
}

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