591. Tag Validator

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, the TAG_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, the TAG_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 of CDATA_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 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.

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

Note:

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

解法1：

此题比较繁琐，题目也巨长。实际上并不是很难。
主要要先总结一下要求：
字符串一定是以tag开头和结尾
tag的名字要符合：　
１．　１－　９个字符之内
２．　只能是upper case letters
３．　需要两两配对
４．　<!出现的话一定需要match ＣＤＡＴＡ

然后对于每一个tag,用一个stack去记录上一个tag的顺序即可。

C++

Java

public class Solution {
    public boolean isValid(String code) {

        // It should start with < and end with >
        if (code == null || code.length() == 0) {
            return false;
        }

        if (code.charAt(0) != '<' || code.charAt(code.length() - 1) != '>') {
            return false;
        }

        Stack<String> stack = new Stack<String>();

        boolean tagExist = false;
        for (int i = 0; i < code.length(); i++) {

            if (stack.isEmpty() && tagExist) {
                return false;
            }
            int last = -1;
            if (code.charAt(i) == '<') {
                if (!stack.isEmpty() && code.charAt(i + 1) == '!') {
                    last = code.indexOf("]]>", i + 1);
                    if (last == -1 || !isValidCdata(code.substring(i + 2, last))) {
                        return false;
                    }
                } else {
                    boolean close = false;
                    if (code.charAt(i + 1) == '/') {
                        close = true;
                        i++;
                    }

                    last = code.indexOf(">", i+1);
                    if (last == -1 || !isValidTagName(code.substring(i + 1, last))) {
                        return false;
                    }
                    if (close) {
                        if (stack.isEmpty() || !stack.peek().equals(code.substring(i + 1, last))) {
                            return false;
                        } else {
                            stack.pop();
                        }
                    } else {
                        tagExist = true;
                        stack.push(code.substring(i + 1, last));
                    }
                }
                i = last;   // move i to the end of the tag
            }
        }

        return stack.isEmpty() && tagExist;

    }

    private boolean isValidCdata(String content) {
        int tag = content.indexOf("[CDATA[");
        return tag == 0;
    }

    private boolean isValidTagName(String tag) {
        int len = tag.length();
        if (len < 1 || len > 9) {
            return false;
        }

        for (int i = 0; i < len; i++) {
            if (tag.charAt(i) < 'A' || tag.charAt(i) > 'Z') {
                return false;
            }
        }
        return true;
    }
}