Tag Validator Python Solution with Tests

lcpy gen -n 591   # by problem number
lcpy gen -s tag_validator   # by problem name

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.

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.

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

class Solution:
    # Time: O(n)
    # Space: O(n)
    def is_valid(self, code: str) -> bool:
        if not code.startswith("<"):
            return False
        stack: list[str] = []
        i = 0
        n = len(code)
        while i < n:
            if stack and code.startswith("<![CDATA[", i):
                end = code.find("]]>", i)
                if end == -1:
                    return False
                i = end + 3
            elif code.startswith("</", i):
                end = code.find(">", i)
                if end == -1:
                    return False
                name = code[i + 2 : end]
                if not stack or stack[-1] != name:
                    return False
                stack.pop()
                i = end + 1
                if not stack and i != n:
                    return False
            elif code.startswith("<", i):
                end = code.find(">", i)
                if end == -1:
                    return False
                name = code[i + 1 : end]
                if not (1 <= len(name) <= 9 and name.isalpha() and name.isupper()):
                    return False
                stack.append(name)
                i = end + 1
            else:
                i += 1
        return not stack