Serialize and Deserialize Binary Tree

• Serialize and Deserialize Binary Tree
  • 题目描述
  • 解法

Serialize and Deserialize Binary Tree

题目描述

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

解法

• 序列化

  代码如下:

    public String serialize(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        StringBuilder sb = new StringBuilder();
        queue.add( root );
        while( !queue.isEmpty() ) {
            TreeNode node = queue.poll();
            if( node == null ) {
                sb.append( '#' );
                continue;
            }
            sb.append( node.val ).append( '#' );
            queue.add( node.left );
            queue.add( node.right );
        }
        return sb.toString();
    }
  

• 反序列化

  代码如下:

    public TreeNode deserialize(String data) {
        Queue<TreeNode> queue = new LinkedList<>();
        int low = 0, high = 0;
        // 获取根节点
        while( high < data.length() && data.charAt( high ) != '#' ) ++high;
        TreeNode root = evalNode( data.substring( low, high ) );
        high = low = high + 1;
  
        queue.add( root );
        while( high < data.length() ) {
            // 获取左子树根节点
            while( high < data.length() && data.charAt( high ) != '#' ) ++high;
            TreeNode left = evalNode( data.substring( low, high ) );
            // 获取右子树根节点
            high = low = high + 1;
            while( high < data.length() && data.charAt( high ) != '#' ) ++high;
            TreeNode right = evalNode( data.substring( low, high ) );
            // 左右子树根节点连接父节点
            TreeNode parent = queue.poll();
            parent.left = left;
            parent.right = right;
            // 加入队列
            if( left != null ) queue.add( left );
            if( right != null ) queue.add( right );
            // 进入下一对
            high = low = high + 1;
        }
        return root;
    }
    private TreeNode evalNode( String s ) {
        Integer val = "".equals( s ) ? null : Integer.parseInt( s );
        return val != null ? new TreeNode( val ) : null;
    }
  

思考过程:

对二叉树进行序列化和反序列化. 首先要定义一个规则, 按照规则进行序列化和反序列化就可以了, 规则如下:

• 对于非空节点, 序列化的结果表示为: val#
• 对于空节点, 序列化的结果表示为: #
• 以层次遍历的顺序把节点序列化和反序列化

时空复杂度: 时间复杂度是O(n), 空间复杂度是O(1)