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:
The code must be wrapped in a valid closed tag. Otherwise, the code is invalid.
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.
A validTAG_NAME only contain upper-case letters , and has length in range [1,9]. Otherwise, the TAG_NAME is invalid.
A validTAG_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.
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.
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).
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]]>.
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.
Input: code ="<DIV>This is the first line <![CDATA[<div>]]></DIV>"Output: trueExplanation:
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 returntrue.
Input: code ="<DIV>>> ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"Output: trueExplanation:
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.
We use a stack to track open tags. For each tag, we check validity and match with the stack. CDATA sections are skipped as plain text. The code is valid if the stack is empty at the end and all rules are satisfied.
We use a stack to track open tags and parse the string character by character. For each tag, we check validity and match with the stack. CDATA sections are skipped as plain text. The code is valid if the stack is empty at the end and all rules are satisfied.