# 331. Verify Preorder Serialization of a Binary Tree LeetCode Solution

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Verify Preorder Serialization of a Binary Tree 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 `','`.

Time: O(n)
Space: O(n)

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