[leetcode]591. Tag Validator
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题目链接:https://leetcode.com/problems/tag-validator/description/
Given a string representing a code snippet, you need to 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.
Valid Code Examples:
Input: "<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 unmatched start tag with invalid TAG_NAME, it should be considered as plain text, not parsed as tag.
So TAG_CONTENT is valid, and then the code is valid. Thus return true.
Input: "<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.
Invalid Code Examples:
Input: "<A> <B> </A> </B>"Output: FalseExplanation: Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa.Input: "<DIV> div tag is not closed <DIV>"Output: FalseInput: "<DIV> unmatched < </DIV>"Output: FalseInput: "<DIV> closed tags with invalid tag name <b>123</b> </DIV>"Output: FalseInput: "<DIV> unmatched tags with invalid tag name </1234567890> and <CDATA[[]]> </DIV>"Output: FalseInput: "<DIV> unmatched start tag <B> and unmatched end tag </C> </DIV>"Output: False
Note:
- For simplicity, you could assume the input code (including the any characters mentioned above) only contain
letters
,digits
,'<'
,'>'
,'/'
,'!'
,'['
,']'
and' '
.
A simple summary for all the elements in this syntax is like this:
tag : <tagname> + content + </tagname>tagname : [A-Z]{1, 9} # 1 ~ 9 uppercase charscontent : (tag|cdata|text)* # 0 or more of : tag, cdata, textcdata : "<![CDATA[" + .* + "]]>"text : [^<]+ # non '<' chars
class Solution {public: bool isValid(string code) { int i = 0; return validTag(code, i) && i == code.size(); }private: bool validTag(string s, int& i) { int j = i; string tag = parseTagName(s, j); if (tag.empty()) return false; if (!validContent(s, j)) return false; int k = j + tag.size() + 2; // expecting j = pos of "</" , k = pos of '>' if (k >= s.size() || s.substr(j, k + 1 - j) != "</" + tag + ">") return false; i = k + 1; return true; } string parseTagName(string s, int& i) { if (s[i] != '<') return ""; int j = s.find('>', i); if (j == string::npos || j - 1 - i < 1 || 9 < j - 1 - i) return ""; string tag = s.substr(i + 1, j - 1 - i); for (char ch : tag) { if (ch < 'A' || 'Z' < ch) return ""; } i = j + 1; return tag; } bool validContent(string s, int& i) { int j = i; while (j < s.size()) { if (!validText(s, j) && !validCData(s, j) && !validTag(s, j)) break; } i = j; return true; } bool validText(string s, int& i) { int j = i; while (i < s.size() && s[i] != '<') { i++; } return i != j; } bool validCData(string s, int& i) { if (s.find("<![CDATA[", i) != i) return false; int j = s.find("]]>", i); if (j == string::npos) return false; i = j + 3; return true; }};
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