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‎Problemset/0591-Tag Validator/README.md

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# 591. Tag Validator
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Given a string representing a code snippet, implement a tag validator to parse the code and return whether it is valid.
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A code snippet is valid if all the following rules hold:
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1. The code must be wrapped in a **valid closed tag**. Otherwise, the code is invalid.
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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.
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3. A **valid** `TAG_NAME` only contain **upper-case letters**, and has length in range [1,9]. Otherwise, the `TAG_NAME` is **invalid**.
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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**.
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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.
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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).
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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** `]]>`.
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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**.
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#### Example 1:
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<pre>
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<strong>Input:</strong> code = "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
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<strong>Output:</strong> true
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<strong>Explanation:</strong>
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The code is wrapped in a closed tag : <DIV> and </DIV>.
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The TAG_NAME is valid, the TAG_CONTENT consists of some characters and cdata.
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Although CDATA_CONTENT has an unmatched start tag with invalid TAG_NAME, it should be considered as plain text, not parsed as a tag.
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So TAG_CONTENT is valid, and then the code is valid. Thus return true.
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</pre>
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#### Example 2:
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<pre>
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<strong>Input:</strong> code = "<DIV>>> ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"
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<strong>Output:</strong> true
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<strong>Explanation:</strong>
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We first separate the code into : start_tag|tag_content|end_tag.
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start_tag -> "<DIV>"
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end_tag -> "</DIV>"
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tag_content could also be separated into : text1|cdata|text2.
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text1 -> ">> ![cdata[]] "
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cdata -> "<![CDATA[<div>]>]]>", where the CDATA_CONTENT is "<div>]>"
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text2 -> "]]>>]"
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The reason why start_tag is NOT "<DIV>>>" is because of the rule 6.
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The reason why cdata is NOT "<![CDATA[<div>]>]]>]]>" is because of the rule 7.
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</pre>
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#### Example 3:
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<pre>
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<strong>Input:</strong> code = "<A> <B> </A> </B>"
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<strong>Output:</strong> false
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<strong>Explanation:</strong> Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa.
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</pre>
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#### Constraints:
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* `1 <= code.length <= 500`
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* `code` consists of English letters, digits, `'<'`, `'>'`, `'/'`, `'!'`, `'['`, `']'`, `'.'`, and `' '`.
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## Solutions (Python)
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### 1. Solution
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```Python
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class Solution:
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def isValid(self, code: str) -> bool:
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cdata = False
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tagstack = []
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i = 0
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while i < len(code):
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if cdata:
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if code[i:i + 3] == "]]>":
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cdata = False
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i += 2
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elif tagstack == [] and (code[i] != '<' or code[i:i + 2] in "</<!"):
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return False
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elif code[i:i + 9] == "<![CDATA[":
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cdata = True
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i += 8
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elif code[i:i + 2] == "</":
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for j in range(i + 2, i + 13):
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if j >= len(code) or j == i + 12 or (j == i + 2 and code[j] == '>'):
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return False
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elif code[j] == '>':
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if tagstack.pop() != code[i + 2:j]:
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return False
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if tagstack == [] and j != len(code) - 1:
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return False
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i = j
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break
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elif not code[j].isupper():
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return False
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elif code[i] == '<':
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for j in range(i + 1, i + 12):
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if j >= len(code) or j == i + 11 or (j == i + 1 and code[j] == '>'):
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return False
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elif code[j] == '>':
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tagstack.append(code[i + 1:j])
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i = j
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break
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elif not code[j].isupper():
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return False
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i += 1
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return tagstack == []
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```

‎Problemset/0591-Tag Validator/README_CN.md

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# 591. 标签验证器
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给定一个表示代码片段的字符串，你需要实现一个验证器来解析这段代码，并返回它是否合法。合法的代码片段需要遵守以下的所有规则：
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1. 代码必须被**合法的闭合标签**包围。否则，代码是无效的。
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2. **闭合标签**（不一定合法）要严格符合格式：`<TAG_NAME>TAG_CONTENT</TAG_NAME>`。其中，`<TAG_NAME>`是起始标签，`</TAG_NAME>`是结束标签。起始和结束标签中的 TAG_NAME 应当相同。当且仅当 TAG_NAME 和 TAG_CONTENT 都是合法的，闭合标签才是**合法的**。
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3. **合法的** `TAG_NAME` 仅含有**大写字母**，长度在范围 [1,9] 之间。否则，该 `TAG_NAME` 是**不合法的**。
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4. **合法的** `TAG_CONTENT` 可以包含其他**合法的闭合标签**，**cdata** （请参考规则7）和任意字符（注意参考规则1）除了不匹配的`<`、不匹配的起始和结束标签、不匹配的或带有不合法 TAG_NAME 的闭合标签。否则，`TAG_CONTENT` 是**不合法的**。
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5. 一个起始标签，如果没有具有相同 TAG_NAME 的结束标签与之匹配，是不合法的。反之亦然。不过，你也需要考虑标签嵌套的问题。
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6. 一个`<`，如果你找不到一个后续的`>`与之匹配，是不合法的。并且当你找到一个`<`或`</`时，所有直到下一个`>`的前的字符，都应当被解析为 TAG_NAME（不一定合法）。
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7. cdata 有如下格式：`<![CDATA[CDATA_CONTENT]]>`。`CDATA_CONTENT` 的范围被定义成 `<![CDATA[` 和**后续的第一个** `]]>`之间的字符。
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8. `CDATA_CONTENT` 可以包含**任意字符**。cdata 的功能是阻止验证器解析`CDATA_CONTENT`，所以即使其中有一些字符可以被解析为标签（无论合法还是不合法），也应该将它们视为**常规字符**。
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#### 合法代码的例子:
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<pre>
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<strong>输入:</strong> "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
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<strong>输出:</strong> True
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<strong>解释:</strong>
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代码被包含在了闭合的标签内： <DIV> 和 </DIV> 。
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TAG_NAME 是合法的，TAG_CONTENT 包含了一些字符和 cdata 。
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即使 CDATA_CONTENT 含有不匹配的起始标签和不合法的 TAG_NAME，它应该被视为普通的文本，而不是标签。
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所以 TAG_CONTENT 是合法的，因此代码是合法的。最终返回True。
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<strong>输入:</strong> "<DIV>>> ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"
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<strong>输出:</strong> True
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<strong>解释:</strong>
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我们首先将代码分割为： start_tag|tag_content|end_tag 。
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start_tag -> "<DIV>"
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end_tag -> "</DIV>"
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tag_content 也可被分割为： text1|cdata|text2 。
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text1 -> ">> ![cdata[]] "
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cdata -> "<![CDATA[<div>]>]]>" ，其中 CDATA_CONTENT 为 "<div>]>"
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text2 -> "]]>>]"
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start_tag 不是 "<DIV>>>" 的原因参照规则 6 。
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cdata 不是 "<![CDATA[<div>]>]]>]]>" 的原因参照规则 7 。
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</pre>
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#### 不合法代码的例子:
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<pre>
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<strong>输入:</strong> "<A> <B> </A> </B>"
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<strong>输出:</strong> False
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<strong>解释:</strong> 不合法。如果 "<A>" 是闭合的，那么 "<B>" 一定是不匹配的，反之亦然。
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<strong>输入:</strong> "<DIV> div tag is not closed <DIV>"
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<strong>输出:</strong> False
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<strong>输入:</strong> "<DIV> unmatched < </DIV>"
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<strong>输出:</strong> False
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<strong>输入:</strong> "<DIV> closed tags with invalid tag name <b>123</b> </DIV>"
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<strong>输出:</strong> False
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<strong>输入:</strong> "<DIV> unmatched tags with invalid tag name </1234567890> and <CDATA[[]]> </DIV>"
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<strong>输出:</strong> False
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<strong>输入:</strong> "<DIV> unmatched start tag <B> and unmatched end tag </C> </DIV>"
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<strong>输出:</strong> False
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</pre>
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#### 注意:
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1. 为简明起见，你可以假设输入的代码（包括提到的**任意字符**）只包含`数字`, `字母`, `'<'`,`'>'`,`'/'`,`'!'`,`'['`,`']'`和`' '`。
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## 题解 (Python)
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### 1. 题解
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```Python
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class Solution:
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def isValid(self, code: str) -> bool:
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cdata = False
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tagstack = []
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i = 0
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while i < len(code):
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if cdata:
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if code[i:i + 3] == "]]>":
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cdata = False
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i += 2
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elif tagstack == [] and (code[i] != '<' or code[i:i + 2] in "</<!"):
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return False
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elif code[i:i + 9] == "<![CDATA[":
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cdata = True
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i += 8
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elif code[i:i + 2] == "</":
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for j in range(i + 2, i + 13):
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if j >= len(code) or j == i + 12 or (j == i + 2 and code[j] == '>'):
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return False
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elif code[j] == '>':
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if tagstack.pop() != code[i + 2:j]:
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return False
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if tagstack == [] and j != len(code) - 1:
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return False
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i = j
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break
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elif not code[j].isupper():
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return False
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elif code[i] == '<':
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for j in range(i + 1, i + 12):
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if j >= len(code) or j == i + 11 or (j == i + 1 and code[j] == '>'):
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return False
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elif code[j] == '>':
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tagstack.append(code[i + 1:j])
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i = j
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break
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elif not code[j].isupper():
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return False
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i += 1
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return tagstack == []
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```

‎Problemset/0591-Tag Validator/Solution.py

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class Solution:
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def isValid(self, code: str) -> bool:
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cdata = False
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tagstack = []
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i = 0
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while i < len(code):
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if cdata:
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if code[i:i + 3] == "]]>":
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cdata = False
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i += 2
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elif tagstack == [] and (code[i] != '<' or code[i:i + 2] in "</<!"):
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return False
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elif code[i:i + 9] == "<![CDATA[":
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cdata = True
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i += 8
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elif code[i:i + 2] == "</":
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for j in range(i + 2, i + 13):
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if j >= len(code) or j == i + 12 or (j == i + 2 and code[j] == '>'):
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return False
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elif code[j] == '>':
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if tagstack.pop() != code[i + 2:j]:
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return False
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if tagstack == [] and j != len(code) - 1:
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return False
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i = j
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break
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elif not code[j].isupper():
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return False
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elif code[i] == '<':
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for j in range(i + 1, i + 12):
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if j >= len(code) or j == i + 11 or (j == i + 1 and code[j] == '>'):
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return False
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elif code[j] == '>':
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tagstack.append(code[i + 1:j])
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i = j
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break
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elif not code[j].isupper():
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return False
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i += 1
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return tagstack == []

‎README.md

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[587][587l] |[Erect the Fence][587] |![rs]
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[589][589l] |[N-ary Tree Preorder Traversal][589] |![py]
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[590][590l] |[N-ary Tree Postorder Traversal][590] |![py]
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[591][591l] |[Tag Validator][591] |![py]
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[592][592l] |[Fraction Addition and Subtraction][592] |![rs]
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[593][593l] |[Valid Square][593] |![rs]
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[594][594l] |[Longest Harmonious Subsequence][594] |![rs]
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[587]:Problemset/0587-Erect%20the%20Fence/README.md#587-erect-the-fence
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[589]:Problemset/0589-N-ary%20Tree%20Preorder%20Traversal/README.md#589-n-ary-tree-preorder-traversal
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[590]:Problemset/0590-N-ary%20Tree%20Postorder%20Traversal/README.md#590-n-ary-tree-postorder-traversal
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[591]:Problemset/0591-Tag%20Validator/README.md#591-tag-validator
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[592]:Problemset/0592-Fraction%20Addition%20and%20Subtraction/README.md#592-fraction-addition-and-subtraction
21032105
[593]:Problemset/0593-Valid%20Square/README.md#593-valid-square
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[594]:Problemset/0594-Longest%20Harmonious%20Subsequence/README.md#594-longest-harmonious-subsequence
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37803782
[587l]:https://leetcode.com/problems/erect-the-fence/
37813783
[589l]:https://leetcode.com/problems/n-ary-tree-preorder-traversal/
37823784
[590l]:https://leetcode.com/problems/n-ary-tree-postorder-traversal/
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[591l]:https://leetcode.com/problems/tag-validator/
37833786
[592l]:https://leetcode.com/problems/fraction-addition-and-subtraction/
37843787
[593l]:https://leetcode.com/problems/valid-square/
37853788
[594l]:https://leetcode.com/problems/longest-harmonious-subsequence/

‎README_CN.md

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[587][587l] |[安装栅栏][587] |![rs]
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[589][589l] |[N叉树的前序遍历][589] |![py]
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[590][590l] |[N叉树的后序遍历][590] |![py]
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[591][591l] |[标签验证器][591] |![py]
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[592][592l] |[分数加减运算][592] |![rs]
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[593][593l] |[有效的正方形][593] |![rs]
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[594][594l] |[最长和谐子序列][594] |![rs]
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[587]:Problemset/0587-Erect%20the%20Fence/README_CN.md#587-安装栅栏
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[589]:Problemset/0589-N-ary%20Tree%20Preorder%20Traversal/README_CN.md#589-n叉树的前序遍历
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[590]:Problemset/0590-N-ary%20Tree%20Postorder%20Traversal/README_CN.md#590-n叉树的后序遍历
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[591]:Problemset/0591-Tag%20Validator/README_CN.md#591-标签验证器
21022104
[592]:Problemset/0592-Fraction%20Addition%20and%20Subtraction/README_CN.md#592-分数加减运算
21032105
[593]:Problemset/0593-Valid%20Square/README_CN.md#593-有效的正方形
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[594]:Problemset/0594-Longest%20Harmonious%20Subsequence/README_CN.md#594-最长和谐子序列
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37803782
[587l]:https://leetcode.cn/problems/erect-the-fence/
37813783
[589l]:https://leetcode.cn/problems/n-ary-tree-preorder-traversal/
37823784
[590l]:https://leetcode.cn/problems/n-ary-tree-postorder-traversal/
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[591l]:https://leetcode.cn/problems/tag-validator/
37833786
[592l]:https://leetcode.cn/problems/fraction-addition-and-subtraction/
37843787
[593l]:https://leetcode.cn/problems/valid-square/
37853788
[594l]:https://leetcode.cn/problems/longest-harmonious-subsequence/

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