591. 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:
- 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 valid
TAG_NAME
only contain upper-case letters, and has length in range [1,9]. Otherwise, theTAG_NAME
is invalid. - 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, theTAG_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 ofCDATA_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 parseCDATA_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.
Constraints:
1 <= code.length <= 500
code
consists of English letters, digits,'<'
,'>'
,'/'
,'!'
,'['
,']'
,'.'
, and' '
.
Solutions
Solution 1
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