leetcode 591. Tag Validator标签验证器 + 解析HTML + 正则表达式

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_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.
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 the subsequent characters until the next > should be parsed as TAG_NAME (not necessarily valid).
The cdata has the following format : . The range of CDATA_CONTENT is defined as the characters between 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.

本题的题意就是解析HTML的标签代码，最好的方法就是使用正则表达式来做，这个很简洁，但是不会做，这个是网上参考的答案

参考的链接是[LeetCode] Tag Validator 标签验证器

代码如下：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

using namespace std;

class Solution 
{
public:
    bool isValid(string code) 
    {
        // inspired by stefanpochmann
        regex cdata(""), tag("<([A-Z]{1,9})>[^<]*");
        code = regex_replace(code, cdata, "c");
        string pre = code;
        while (pre != (code = regex_replace(code, tag, "t"))) 
            pre = code;
        return "t" == code;
    }
};