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 ' '.
Solution:
class Solution {
public boolean isValid(String code) {
int n = code.length();
Deque<String> tags = new ArrayDeque();
boolean startTag = false, endTag = false, codeClosed = false;
StringBuilder tag = new StringBuilder();
for (int i = 0; i < n; i ++) {
if (codeClosed) {
System.out.println("code closed");
return false;
}
char c = code.charAt(i);
if (c == '<') {
if (i + 9 < n && code.substring(i, i + 9).equals("<![CDATA[")) {
if (tags.isEmpty()) {
System.out.println("CDATA not inside a tag");
return false;
}
int endOfCDATA = code.indexOf("]]>", i + 9);
if (endOfCDATA == -1) {
System.out.println("endOfCDATA");
return false;
}
i = endOfCDATA + 2;
} else if (startTag || endTag) {
System.out.println("< inside tag");
return false;
} else if (i + 1 < n && code.charAt(i + 1) == '/') {
i ++;
endTag = true;
} else if (!startTag) {
startTag = true;
}
continue;
}
if (c == '>') {
if (startTag) {
startTag = false;
if (tag.length() == 0 || tag.length() > 9) {
System.out.println("tagLength > 9 or == 0");
return false;
}
tags.push(tag.toString());
tag.setLength(0);
startTag = false;
} else if (endTag) {
String eTag = tag.toString();
if (tags.isEmpty()) {
System.out.println("noStartTag");
return false;
}
String sTag = tags.pop();
if (!sTag.equals(eTag)) {
System.out.println(sTag + ", " + eTag + ": tags do not match");
return false;
}
tag.setLength(0);
if (tags.isEmpty()) {
codeClosed = true;
}
endTag = false;
}
continue;
}
if (startTag || endTag) {
if (!Character.isLetter(c) || !Character.isUpperCase(c)) {
System.out.println(c + ": tagname not valid");
return false;
}
tag.append(c);
continue;
}
if (tags.isEmpty()) {
System.out.println(c + ": not in tag content" + ", " + i);
return false;
}
}
return !startTag && !endTag && tags.isEmpty();
}
}