問題:app
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.less
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.ui
For example, you may serialize the following treethis
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.spa
Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.rest
解決:code
① 理論上說全部遍歷的方法均可以。orm
可是爲了使serialize和deserialize的過程都儘可能最簡單,preorder是不錯的選擇。serialize的話,dfs比較好寫,deserialize的話preorder和bfs比較好寫。用「,」做爲分隔符,「#」來表示null。例子裏serialize以後結果就變成"1,2,3,#,#,4,5"。deserialize的時候用一個queue來保存string。leetcode
Time: O(N), Space: O(N)get
public class Codec { //25ms // Encodes a tree to a single string. public String serialize(TreeNode root) { if (root == null) return ""; StringBuilder encodedStr = new StringBuilder(); encode(root,encodedStr); return encodedStr.substring(1).toString(); } public void encode(TreeNode root,StringBuilder sb){ if (root == null){ sb.append(",#"); return; } sb.append(",").append(root.val); encode(root.left,sb); encode(root.right,sb); } // Decodes your encoded data to tree. public TreeNode deserialize(String data) { if (data.length() == 0) return null; Queue<String> queue = new LinkedList<>(Arrays.asList(data.split(","))); return decode(queue); } public TreeNode decode(Queue<String> queue){ if (queue.isEmpty()) return null; String cur = queue.poll(); if (cur.equals("#")) return null; TreeNode root = new TreeNode(Integer.valueOf(cur)); root.left = decode(queue); root.right = decode(queue); return root; } } // Your Codec object will be instantiated and called as such: // Codec codec = new Codec(); // codec.deserialize(codec.serialize(root));