# 0591. Tag Validator

<https://leetcode.com/problems/tag-validator>

## Description

Given a string representing a code snippet, implement a tag validator to parse the code and return whether it is valid.

A code snippet is valid if all the following rules hold:

1. The code must be wrapped in a **valid closed tag**. Otherwise, the code is invalid.
2. A **closed tag** (not necessarily valid) has exactly the following format : `<TAG_NAME>TAG_CONTENT</TAG_NAME>`. Among them, `<TAG_NAME>` is the start tag, and `</TAG_NAME>` is the end tag. The TAG\_NAME in start and end tags should be the same. A closed tag is **valid** if and only if the TAG\_NAME and TAG\_CONTENT are valid.
3. A **valid** `TAG_NAME` only contain **upper-case letters**, and has length in range \[1,9]. Otherwise, the `TAG_NAME` is **invalid**.
4. A **valid** `TAG_CONTENT` may contain other **valid closed tags**, **cdata** and any characters (see note1) **EXCEPT** unmatched `<`, unmatched start and end tag, and unmatched or closed tags with invalid TAG\_NAME. Otherwise, the `TAG_CONTENT` is **invalid**.
5. A start tag is unmatched if no end tag exists with the same TAG\_NAME, and vice versa. However, you also need to consider the issue of unbalanced when tags are nested.
6. A `<` is unmatched if you cannot find a subsequent `>`. And when you find a `<` or `</`, all the subsequent characters until the next `>` should be parsed as TAG\_NAME (not necessarily valid).
7. The cdata has the following format : `<![CDATA[CDATA_CONTENT]]>`. The range of `CDATA_CONTENT` is defined as the characters between `<![CDATA[` and the **first subsequent** `]]>`.
8. `CDATA_CONTENT` may contain **any characters**. The function of cdata is to forbid the validator to parse `CDATA_CONTENT`, so even it has some characters that can be parsed as tag (no matter valid or invalid), you should treat it as **regular characters**.

**Example 1:**

```
**Input:** code = "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
**Output:** true
**Explanation:** 
The code is wrapped in a closed tag : <DIV> and </DIV>. 
The TAG\_NAME is valid, the TAG\_CONTENT consists of some characters and cdata. 
Although CDATA\_CONTENT has an unmatched start tag with invalid TAG\_NAME, it should be considered as plain text, not parsed as a tag.
So TAG\_CONTENT is valid, and then the code is valid. Thus return true.
```

**Example 2:**

```
**Input:** code = "<DIV>>>  ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"
**Output:** true
**Explanation:**
We first separate the code into : start\_tag|tag\_content|end\_tag.
start\_tag -> **"<DIV>"**
end\_tag -> **"</DIV>"**
tag\_content could also be separated into : text1|cdata|text2.
text1 -> **">> ![cdata[]] "**
cdata -> **"<![CDATA[<div>]>]]>"**, where the CDATA\_CONTENT is **"<div>]>"**
text2 -> **"]]>>]"**
The reason why start\_tag is NOT **"<DIV>>>"** is because of the rule 6.
The reason why cdata is NOT **"<![CDATA[<div>]>]]>]]>"** is because of the rule 7.
```

**Example 3:**

```
**Input:** code = "<A>  <B> </A>   </B>"
**Output:** false
**Explanation:** Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa.
```

**Example 4:**

```
**Input:** code = "<DIV>  div tag is not closed  <DIV>"
**Output:** false
```

**Constraints:**

* `1 <= code.length <= 500`
* `code` consists of English letters, digits, `'<'`, `'>'`, `'/'`, `'!'`, `'['`, `']'`, `'.'`, and `' '`.

## ac

```java
```