Serialize and Deserialize Binary Tree
Description
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 tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.
For example, you may serialize the following tree
1
/ \ 2 3 / \ 4 5 as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.
Hint
Train of Thought
The idea is simple: print the tree in pre-order traversal and use "X" to denote null node and split node with ",". We can use a StringBuilder for building the string on the fly. For deserializing, we use a Queue to store the pre-order traversal and since we have "X" as null node, we know exactly how to where to end building subtress.
Code
public String serialize(TreeNode root) {
return serial(new StringBuilder(), root).toString();
}
private StringBuilder serial(StringBuilder str, TreeNode root) {
if (root == null) return str.append("#");
str.append(root.val).append(",");
serial(str, root.left).append(","); // note execution order
return serial(str, root.right);
}
public TreeNode deserialize(String data) {
return deserial(new LinkedList<>(Arrays.asList(data.split(","))));
}
private TreeNode deserial(Queue<String> queue) {
String val = queue.poll(); // return null if empty
if ("#".equals(val)) return null;
TreeNode root = new TreeNode(Integer.valueOf(val));
root.left = deserial(queue);
root.right = deserial(queue);
return root;
}