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331. Verify Preorder Serialization of a Binary Tree.go
331. Verify Preorder Serialization of a Binary Tree_test.go

# 331. Verify Preorder Serialization of a Binary Tree

## 题目

One way to serialize a binary tree is to use pre-order 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 #.

```     _9_
/   \
3     2
/ \   / \
4   1  #  6
/ \ / \   / \
# # # #   # #```

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, verify whether it is a correct preorder traversal serialization of a binary tree. Find an algorithm without reconstructing the tree.

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".

Example 1:

```Input: "9,3,4,#,#,1,#,#,2,#,6,#,#"
Output: true```

Example 2:

```Input: "1,#"
Output: false```

Example 3:

```Input: "9,#,#,1"
Output: false```

## 解题思路

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