剑指offer -- 序列化二叉树

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

AC代码1

曾经见到过一个非常令人吃惊的代码。
因为题目中没有规定序列化的方法，因此没办法检验序列化后结果的正确性，这也正是BUG所在。

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

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    TreeNode root = null;
    String Serialize(TreeNode root) {
        this.root = root;
        return null;
  }
    TreeNode Deserialize(String str) {
       return this.root;
  }
}

AC代码2

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

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {

    String Serialize(TreeNode root) {
        if(root == null)
            return "";
        StringBuilder sb = new StringBuilder();
        SerializeCore(root, sb);
        return sb.toString();
    }
     
    void SerializeCore(TreeNode root, StringBuilder sb) {
        if(root == null) {
            sb.append("$,");
            return;
        }
        sb.append(root.val);
        sb.append(',');
        SerializeCore(root.left, sb);
        SerializeCore(root.right, sb);
    }
    int start = 0;
    TreeNode Deserialize(String str) {
        if(str.equals("")) return null;
        return DeserializeCore(str);
  }
    
    private TreeNode DeserializeCore(String str){
        if(start == str.length()) return null;
        int ch = str.charAt(start);
        if(ch == '$') {
            start++;
            start++;
            return null;
        }
        TreeNode root = new TreeNode(0);
        int val = 0;
        while(ch >= '0' && ch <= '9'){
            val = val * 10 + (ch - '0');
            start++;
            ch = str.charAt(start);
        }
        start++;
        root.val = val;
        root.left = DeserializeCore(str);
        root.right = DeserializeCore(str);
        return root;
    }
}