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:
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.
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
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