【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