#数据结构与算法学习笔记#剑指Offer59：线索化/序列化二叉树（Java、C/C++）

2019.2.28     《剑指Offer》从零单刷个人笔记整理（66题全）目录传送门

二叉树序列化的意思是按照某种遍历顺序及某种特定格式保存为字符串。

例如对于一棵0-6层序的满二叉树，遇到null则保存为‘#’，每次结点结束标‘！’，则序列化的结果为：

0!1!3!#!#!4!#!#!2!5!#!#!6!#!#!

 那序列化很简单，只要按遍历的过程给StringBuilder赋值即可。

反序列化则需要设置一个全局计数器（或者用计数器作为函数的一个形参）进行递归。

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题目描述

请实现两个函数，分别用来序列化和反序列化二叉树

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Java实现：

/**
 * 
 * @author ChopinXBP
 * 请实现两个函数，分别用来序列化和反序列化二叉树
 *
 */

public class SerializeTree_60 {

	public static class TreeNode {
	    int val = 0;
	    TreeNode left = null;
	    TreeNode right = null;

	    public TreeNode(int val) {
	        this.val = val;
	    }
	}
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeNode pHead = new TreeNode(0);
		TreeNode p1= new TreeNode(1);
		TreeNode p2= new TreeNode(2);
		TreeNode p3= new TreeNode(3);
		TreeNode p4= new TreeNode(4);
		TreeNode p5= new TreeNode(5);
		TreeNode p6= new TreeNode(6);
		pHead.left = p1;
		pHead.right = p2;
		p1.left = p3;
		p1.right = p4;
		p2.left = p5;
		p2.right = p6;
		
		String result = Serialize(pHead);
		System.out.println(result);
		pHead = Deserialize(result);
		
	}

	public static String Serialize(TreeNode root) {
        if(root == null) return null;
		StringBuilder str = new StringBuilder();
		strBuild(root, str);
		return str.toString();
    }
	
	public static void strBuild(TreeNode root, StringBuilder str) {
		if(root == null) {
			str.append("#!");	//用‘#’代表null结点
			return;
		}
		str.append(root.val + "!");
		strBuild(root.left, str);
		strBuild(root.right, str);
	}
    
	private static int idx;
	
	public static TreeNode Deserialize(String str) {
        TreeNode root = null;
		if(str == null)return root;
       
		String[] strings = str.split("!");
		if(strings.length == 0) return root;
		
		idx = -1;
		root = treeBuild(strings);
		
        return root;
    }
	
	public static TreeNode treeBuild(String[] strings) {
		if(idx > strings.length) {
			return null;
		}
		idx++;
		TreeNode node = null;
		if(!strings[idx].equals("#")) {
			node = new TreeNode(Integer.parseInt(strings[idx]));
			node.left = treeBuild(strings);
			node.right = treeBuild(strings);
		}		
		return node;
	}
}

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C++实现示例：

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;
 
    public TreeNode(int val) {
        this.val = val;
 
    }
 
}
*/
public class Solution {
    public int index = -1;
    String Serialize(TreeNode root) {
        StringBuffer sb = new StringBuffer();
        if(root == null){
            sb.append("#,");
            return sb.toString();
        }
        sb.append(root.val + ",");
        sb.append(Serialize(root.left));
        sb.append(Serialize(root.right));
        return sb.toString();
  }
    TreeNode Deserialize(String str) {
        index++;
       int len = str.length();
        if(index >= len){
            return null;
        }
        String[] strr = str.split(",");
        TreeNode node = null;
        if(!strr[index].equals("#")){
            node = new TreeNode(Integer.valueOf(strr[index]));
            node.left = Deserialize(str);
            node.right = Deserialize(str);
        }
         
        return node;
  }
}

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