Binary Tree Serialization

 1 /**
 2  * Definition of TreeNode:
 3  * public class TreeNode {
 4  *     public int val;
 5  *     public TreeNode left, right;
 6  *     public TreeNode(int val) {
 7  *         this.val = val;
 8  *         this.left = this.right = null;
 9  *     }
10  * }
11  */
12 class Solution {
13     /**
14      * This method will be invoked first, you should design your own algorithm 
15      * to serialize a binary tree which denote by a root node to a string which
16      * can be easily deserialized by your own "deserialize" method later.
17      */
18     public String serialize(TreeNode root) {
19         if (root == null) return "";
20         StringBuilder pre = new StringBuilder();
21         StringBuilder in = new StringBuilder();
22 
23         preOrder(root, pre);
24         inOrder(root, in);
25 
26         String all = pre.substring(0, pre.length() - 1) + "@" + in.substring(0, pre.length() - 1);
27         return all;
28     }
29 
30     public void preOrder(TreeNode root, StringBuilder pre) {
31         if (root != null) {
32             pre.append(root.val + ",");
33             preOrder(root.left, pre);
34             preOrder(root.right, pre);
35         }
36     }
37 
38     public void inOrder(TreeNode root, StringBuilder str) {
39         if (root != null) {
40             inOrder(root.left, str);
41             str.append(root.val + ",");
42             inOrder(root.right, str);
43         }
44     }
45 
46     /**
47      * This method will be invoked second, the argument data is what exactly you
48      * serialized at method "serialize", that means the data is not given by
49      * system, it‘s given by your own serialize method. So the format of data is
50      * designed by yourself, and deserialize it here as you serialize it in
51      * "serialize" method.
52      */
53     public TreeNode deserialize(String data) {
54         if (data.equals("")) return null;
55         int index = data.indexOf("@");
56         String[] pre = data.substring(0, index).split(",");
57         String[] mid = data.substring(index + 1).split(",");
58         return createTree(pre, 0, mid, 0, pre.length);
59     }
60 
61     public TreeNode createTree(String[] preString, int preStart, String[] inString, int inStart, int length) {
62 
63         if (length <= 0) return null;
64 
65         TreeNode root = new TreeNode(Integer.parseInt(preString[preStart]));
66 
67         int index = findIndex(inString, root.val + "");
68         root.left = createTree(preString, preStart + 1, inString, inStart, index - inStart);
70         root.right = createTree(preString, preStart + (index - inStart) + 1, inString, index + 1, length - (index - inStart) - 1);
72 
73         return root;
74     }
75 
76     public int findIndex(String[] str, String val) {
77         for (int i = 0; i < str.length; i++) {
78             if (str[i].equals(val)) {
79                 return i;
80             }
81         }
82         return -1;
83     }
84 }