【LeetCode】449.Serialize and Deserialize BST(Medium)解题报告

【LeetCode】449.Serialize and Deserialize BST(Medium)解题报告

题目地址：https://leetcode.com/problems/serialize-and-deserialize-bst/description/
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 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.

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 前面二叉树的方法同样适用，但是此题我们根据二叉搜索树的性质
 先序遍历，queue
 */
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if(root == null) return "";
        StringBuilder res = new StringBuilder();
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        while(!stack.isEmpty()){
            TreeNode cur = stack.pop();
            res.append(cur.val+" ");
            if(cur.right != null) stack.push(cur.right);
            if(cur.left != null) stack.push(cur.left);
        }
        return res.toString();     
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if(data == "") return null;
        String[] str = data.split(" ");
        Queue<Integer> queue = new LinkedList<>();
        for(String s : str){
            queue.offer(Integer.parseInt(s));
        }
        return getNode(queue);
    }
    public TreeNode getNode(Queue<Integer> queue){
        if(queue.isEmpty()) return null;
        TreeNode root = new TreeNode(queue.poll());
        Queue<Integer> smallerQ = new LinkedList<>();
        while(!queue.isEmpty() && queue.peek() < root.val){
            smallerQ.offer(queue.poll());
        }
        root.left = getNode(smallerQ);
        root.right = getNode(queue);
        return root;
    }
}

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

Date：2018年3月29日