1. 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:

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_CONTENT. Among them, is the start tag, and 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 : 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.

Note:

For simplicity, you could assume the input code (including the any characters mentioned above) only contain letters, digits, '<','>','/','!','[',']' and ' '.

2. Runtime Distribution

3. Submission Details

4. Example

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: False
Explanation: Unbalanced. If <A> is closed, then <B> must be unmatched, and vice versa.
Input: <DIV> div tag is not closed <DIV>
Output: False
Input: <DIV> unmatched < </DIV>
Output: False
Input: <DIV> closed tags with invalid tag name <b>123</b> </DIV>
Output: False
Input: <DIV> unmatched tags with invalid tag name </1234567890> and <CDATA[[]]> </DIV>
Output: False
Input: <DIV> unmatched start tag <B> and unmatched end tag </C> </DIV>
Output: False

5. Code

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public boolean isValid(String code) {

	if (code == null || code.length() == 0) {
		return true;
	}

	if (code.startsWith(" stack = new Stack();

	String sub = "";
	for (int i = 0; i < code.length(); i++) {

		sub += code.charAt(i);
		if (!sub.startsWith("<")) {
			sub = "";
			continue;
		}

		if (sub.startsWith("")) {
				String tagName = sub.substring(2, sub.length() - 1);
				if (stack.isEmpty() || !stack.pop().equals(tagName)) {
					return false;
				}

				if (i < code.length() - 1 && stack.isEmpty()) {
					return false;
				}
				sub = "";
			}
		} else if (sub.startsWith("<")) {
			if (sub.endsWith(">")) {
				String tagName = sub.substring(1, sub.length() - 1);
				if (!checkTagName(tagName)) {
					return false;
				}
				stack.add(tagName);
				sub = "";
			}
		}
	}

	return stack.isEmpty() && sub.length() == 0;
}

private boolean checkTagName(String tagName) {
	if (tagName.length() > 9 || tagName.length() < 1) {
		return false;
	}
	for (int i = 0; i < tagName.length(); i++) {
		if (!Character.isUpperCase(tagName.charAt(i))) {
			return false;
		}
	}
	return true;
}

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6.Test

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import java.util.Stack;

public class LeetCode0591 {

	public boolean isValid(String code) {

		if (code == null || code.length() == 0) {
			return true;
		}

		if (code.startsWith(" stack = new Stack();

		String sub = "";
		for (int i = 0; i < code.length(); i++) {

			sub += code.charAt(i);
			if (!sub.startsWith("<")) {
				sub = "";
				continue;
			}

			if (sub.startsWith("")) {
					String tagName = sub.substring(2, sub.length() - 1);
					if (stack.isEmpty() || !stack.pop().equals(tagName)) {
						return false;
					}

					if (i < code.length() - 1 && stack.isEmpty()) {
						return false;
					}
					sub = "";
				}
			} else if (sub.startsWith("<")) {
				if (sub.endsWith(">")) {
					String tagName = sub.substring(1, sub.length() - 1);
					if (!checkTagName(tagName)) {
						return false;
					}
					stack.add(tagName);
					sub = "";
				}
			}
		}

		return stack.isEmpty() && sub.length() == 0;
	}

	private boolean checkTagName(String tagName) {
		if (tagName.length() > 9 || tagName.length() < 1) {
			return false;
		}
		for (int i = 0; i < tagName.length(); i++) {
			if (!Character.isUpperCase(tagName.charAt(i))) {
				return false;
			}
		}
		return true;
	}

	public static void main(String[] args) {
		LeetCode0591 leetcode = new LeetCode0591();
		System.out.println(leetcode.isValid(""));
	}
}

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