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_NAMEonly contain upper-case letters, and has length in range [1,9]. Otherwise, theTAG_NAMEis invalid. - A valid
TAG_CONTENTmay 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, theTAG_CONTENTis 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 ofCDATA_CONTENTis defined as the characters between<![CDATA[and the first subsequent]]>. CDATA_CONTENTmay contain any characters. The function of cdata is to forbid the validator to parseCDATA_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' '.
题目理解：判断一个半结构化语句是否正确，语句结构要求不意义解读，只强调以下cdata部分，格式是<![CDATA[******]]>
解题思路：
1.掐头去尾，得到语句内容，同时检测开始标签和结束标签的合法性
2.检测语句内容的合法性：
2.1 直接删除cdata部分和第一个'<'之前的部分，这些部分一定合法，将剩余部分存储到rest字符串中
2.2 如果rest不为空，那么rest一定以一个开始标签开头，因此再次掐头去尾，得到语句内容和除去当前闭合标签之外的部分，对两部分作为语句内容，分别检查合法性
注意一种特殊情况：<A></A><A></A>和<A><A></A></A>，这两种语句都是正确的，需要找一个合适的方法来匹配开始和结束标签，这里，我使用的方法是，对于一个开始标签startTag，找到其最右边的出现位置，与这个位置的startTag匹配的endTag一定是它右边紧邻的第一个endTag
class Solution {
public boolean isValid(String code) {
if(code.length() == 0)
return true;
//取得start tag
int pos = code.indexOf('<');
if(pos != 0)
return false;
pos = code.indexOf('>');
if(pos == -1)
return false;
String startTag = code.substring(0, pos + 1);
if(startTag.length() > 11 || startTag.length() < 3)
return false;
for(int i = 1; i < startTag.length() - 1; i++){
char ch = startTag.charAt(i);
if(ch > 'Z' || ch < 'A')
return false;
}
String endTag = "</" + startTag.substring(1);
//取得当前语句，并对剩余语句进行递归处理
if(!code.endsWith(endTag))
return false;
//处理语句内容
String content = code.substring(startTag.length(), code.length() - endTag.length());
if(!doContent(content))
return false;
return true;
}
public boolean doContent(String code){
//System.out.println(code);
//取得start tag，这时代码可以不是start tag开头
//去掉CDATA
int start = code.indexOf("<![CDATA["), end = code.indexOf("]]>");
while(start != -1 && end != -1){
code = code.substring(0, start) + code.substring(end + 3);
start = code.indexOf("<![CDATA[");
end = code.indexOf("]]>");
}
//去掉<之前的内容，即任意非保留字符，如果不含有<，则说明不含有任何保留字符，即为真
int pos = code.indexOf('<');
if(pos == -1)
return true;
if(pos != 0)
code = code.substring(pos);
//如果执行到这里，说明内容中还包含有闭合语句
//取得start tag
pos = code.indexOf('>');
if(pos == -1)
return false;
String startTag = code.substring(0, pos + 1);
if(startTag.length() > 11 || startTag.length() < 3)
return false;
for(int i = 1; i < startTag.length() - 1; i++){
char ch = startTag.charAt(i);
if(ch > 'Z' || ch < 'A')
return false;
}
String endTag = "</" + startTag.substring(1);
//取得语句内容，并对剩余语句进行递归处理
start = 0;
int temp = code.indexOf(startTag, start + 1);
while(temp != -1){
start = temp;
temp = code.indexOf(startTag, start + 1);
}
end = code.indexOf(endTag, start + 1);
if(end == -1)
return false;
String rest = code.substring(0, start) + code.substring(end + endTag.length());
if(!doContent(rest))
return false;
//处理语句内容
String content = code.substring(start + startTag.length(), end);
if(!doContent(content))
return false;
return true;
}
}