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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:

  1. The code must be wrapped in a valid closed tag. Otherwise, the code is invalid.
  2. 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.
  3. A valid TAG_NAME only contain upper-case letters, and has length in range [1,9]. Otherwise, the TAG_NAME is invalid.
  4. 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, the TAG_CONTENT is invalid.
  5. 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.
  6. 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).
  7. 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 ]]>.
  8. 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.

 

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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class Solution:
    def isValid(self, code: str) -> bool:
        def check(tag):
            return 1 <= len(tag) <= 9 and all(c.isupper() for c in tag)

        stk = []
        i, n = 0, len(code)
        while i < n:
            if i and not stk:
                return False
            if code[i : i + 9] == '<![CDATA[':
                i = code.find(']]>', i + 9)
                if i < 0:
                    return False
                i += 2
            elif code[i : i + 2] == '</':
                j = i + 2
                i = code.find('>', j)
                if i < 0:
                    return False
                t = code[j:i]
                if not check(t) or not stk or stk.pop() != t:
                    return False
            elif code[i] == '<':
                j = i + 1
                i = code.find('>', j)
                if i < 0:
                    return False
                t = code[j:i]
                if not check(t):
                    return False
                stk.append(t)
            i += 1
        return not stk
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class Solution {
    public boolean isValid(String code) {
        Deque<String> stk = new ArrayDeque<>();
        for (int i = 0; i < code.length(); ++i) {
            if (i > 0 && stk.isEmpty()) {
                return false;
            }
            if (code.startsWith("<![CDATA[", i)) {
                i = code.indexOf("]]>", i + 9);
                if (i < 0) {
                    return false;
                }
                i += 2;
            } else if (code.startsWith("</", i)) {
                int j = i + 2;
                i = code.indexOf(">", j);
                if (i < 0) {
                    return false;
                }
                String t = code.substring(j, i);
                if (!check(t) || stk.isEmpty() || !stk.pop().equals(t)) {
                    return false;
                }
            } else if (code.startsWith("<", i)) {
                int j = i + 1;
                i = code.indexOf(">", j);
                if (i < 0) {
                    return false;
                }
                String t = code.substring(j, i);
                if (!check(t)) {
                    return false;
                }
                stk.push(t);
            }
        }
        return stk.isEmpty();
    }

    private boolean check(String tag) {
        int n = tag.length();
        if (n < 1 || n > 9) {
            return false;
        }
        for (char c : tag.toCharArray()) {
            if (!Character.isUpperCase