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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(c)) {
                return false;
            }
        }
        return true;
    }
}

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class Solution {
public:
    bool isValid(string code) {
        stack<string> stk;
        for (int i = 0; i < code.size(); ++i) {
            if (i && stk.empty()) return false;
            if (code.substr(i, 9) == "<![CDATA[") {
                i = code.find("]]>", i + 9);
                if (i < 0) return false;
                i += 2;
            } else if (code.substr(i, 2) == "</") {
                int j = i + 2;
                i = code.find('>', j);
                if (i < 0) return false;
                string t = code.substr(j, i - j);
                if (!check(t) || stk.empty() || stk.top() != t) return false;
                stk.pop();
            } else if (code.substr(i, 1) == "<") {
                int j = i + 1;
                i = code.find('>', j);
                if (i < 0) return false;
                string t = code.substr(j, i - j);
                if (!check(t)) return false;
                stk.push(t);
            }
        }
        return stk.empty();
    }

    bool check(string tag) {
        int n = tag.size();
        if (n < 1 || n > 9) return false;
        for (char& c : tag)
            if (!isupper(c))
                return false;
        return true;
    }
};

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func isValid(code string) bool {
    var stk []string
    for i := 0; i < len(code); i++ {
        if i > 0 && len(stk) == 0 {
            return false
        }
        if strings.HasPrefix(code[i:], "<![CDATA[") {
            n := strings.Index(code[i+9:], "]]>")
            if n == -1 {
                return false
            }
            i += n + 11
        } else if strings.HasPrefix(code[i:], "</") {
            if len(stk) == 0 {
                return false
            }
            j := i + 2
            n := strings.IndexByte(code[j:], '>')
            if n == -1 {
                return false
            }
            t := code[j : j+n]
            last := stk[len(stk)-1]
            stk = stk[:len(stk)-1]
            if !check(t) || last != t {
                return false
            }
            i += n + 2
        } else if strings.HasPrefix(code[i:], "<") {
            j := i + 1
            n := strings.IndexByte(code[j:], '>')
            if n == -1 {
                return false
            }
            t := code[j : j+n]
            if !check(t) {
                return false
            }
            stk = append(stk, t)
            i += n + 1
        }
    }
    return len(stk) == 0
}

func check(tag string) bool {
    n := len(tag)
    if n < 1 || n > 9 {
        return false
    }
    for _, c := range tag {
        if c < 'A' || c > 'Z' {
            return false
        }
    }
    return true
}

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impl Solution {
    pub fn is_valid(code: String) -> bool {
        fn check(tag: &str) -> bool {
            let n = tag.len();
            n >= 1 && n <= 9 && tag.as_bytes().iter().all(|b| b.is_ascii_uppercase())
        }

        let mut stk = Vec::new();
        let mut i = 0;
        while i < code.len() {
            if i > 0 && stk.is_empty() {
                return false;
            }
            if code[i..].starts_with("<![CDATA[") {
                match code[i + 9..].find("]]>") {
                    Some(n) => {
                        i += n + 11;
                    }
                    None => {
                        return false;
                    }
                };
            } else if code[i..].starts_with("</") {
                let j = i + 2;
                match code[j..].find('>') {
                    Some(n) => {
                        let t = &code[j..j + n];
                        if !check(t) || stk.is_empty() || stk.pop().unwrap() != t {
                            return false;
                        }
                        i += n + 2;
                    }
                    None => {
                        return false;
                    }
                };
            } else if code[i..].starts_with("<") {
                let j = i + 1;
                match code[j..].find('>') {
                    Some(n) => {
                        let t = &code[j..j + n];
                        if !check(t) {
                            return false;
                        }
                        stk.push(t);
                    }
                    None => {
                        return false;
                    }
                };
            }
            i += 1;
        }
        stk.is_empty()
    }
}

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