Hard
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:
<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.TAG_NAME
only contain upper-case letters, and has length in range [1,9]. Otherwise, the TAG_NAME
is invalid.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.<
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).<![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.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> ”
Output: false
Explanation: Unbalanced. If “” is closed, then “” must be unmatched, and vice versa.
Constraints:
1 <= code.length <= 500
code
consists of English letters, digits, '<'
, '>'
, '/'
, '!'
, '['
, ']'
, '.'
, and ' '
.import java.util.ArrayDeque;
import java.util.Deque;
public class Solution {
public boolean isValid(String code) {
Deque<String> stack = new ArrayDeque<>();
int i = 0;
while (i < code.length()) {
if (i > 0 && stack.isEmpty()) {
return false;
}
if (code.startsWith("<![CDATA[", i)) {
// "<![CDATA[" length is 9
int j = i + 9;
i = code.indexOf("]]>", j);
if (i < 0) {
return false;
}
// "]]>" length is 3
i += 3;
} else if (code.startsWith("</", i)) {
int j = i + 2;
i = code.indexOf(">", j);
if (i < 0 || i == j || i - j > 9) {
return false;
}
for (int k = j; k < i; k++) {
if (!Character.isUpperCase(code.charAt(k))) {
return false;
}
}
String s = code.substring(j, i++);
if (stack.isEmpty() || !stack.pop().equals(s)) {
return false;
}
} else if (code.startsWith("<", i)) {
int j = i + 1;
i = code.indexOf(">", j);
if (i < 0 || i == j || i - j > 9) {
return false;
}
for (int k = j; k < i; k++) {
if (!Character.isUpperCase(code.charAt(k))) {
return false;
}
}
String s = code.substring(j, i++);
stack.push(s);
} else {
i++;
}
}
return stack.isEmpty();
}
}