public class Solution
extends Object
331 - Verify Preorder Serialization of a Binary Tree\.
Medium
One way to serialize a binary tree is to use **preorder traversal**. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as `'#'`.
For example, the above binary tree can be serialized to the string `"9,3,4,#,#,1,#,#,2,#,6,#,#"`, where `'#'` represents a null node.
Given a string of comma-separated values `preorder`, return `true` if it is a correct preorder traversal serialization of a binary tree.
It is **guaranteed** that each comma-separated value in the string must be either an integer or a character `'#'` representing null pointer.
You may assume that the input format is always valid.
* For example, it could never contain two consecutive commas, such as `"1,,3"`.
**Note: **You are not allowed to reconstruct the tree.
**Example 1:**
**Input:** preorder = "9,3,4,#,#,1,#,#,2,#,6,#,#"
**Output:** true
**Example 2:**
**Input:** preorder = "1,#"
**Output:** false
**Example 3:**
**Input:** preorder = "9,#,#,1"
**Output:** false
**Constraints:**
* 1 <= preorder.length <= 104
* `preorder` consist of integers in the range `[0, 100]` and `'#'` separated by commas `','`.