<p><strong>HTML entity parser</strong> is the parser that takes HTML code as input and replace all the entities of the special characters by the characters itself.</p>

<p>The special characters and their entities for HTML are:</p>

<ul>
	<li><strong>Quotation Mark:</strong> the entity is <code>&amp;quot;</code> and symbol character is <code>&quot;</code>.</li>
	<li><strong>Single Quote Mark:</strong> the entity is <code>&amp;apos;</code> and symbol character is <code>&#39;</code>.</li>
	<li><strong>Ampersand:</strong> the entity is <code>&amp;amp;</code> and symbol character is <code>&amp;</code>.</li>
	<li><strong>Greater Than Sign:</strong> the entity is <code>&amp;gt;</code> and symbol character is <code>&gt;</code>.</li>
	<li><strong>Less Than Sign:</strong> the entity is <code>&amp;lt;</code> and symbol character is <code>&lt;</code>.</li>
	<li><strong>Slash:</strong> the entity is <code>&amp;frasl;</code> and symbol character is <code>/</code>.</li>
</ul>

<p>Given the input <code>text</code> string to the HTML parser, you have to implement the entity parser.</p>

<p>Return <em>the text after replacing the entities by the special characters</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> text = &quot;&amp;amp; is an HTML entity but &amp;ambassador; is not.&quot;
<strong>Output:</strong> &quot;&amp; is an HTML entity but &amp;ambassador; is not.&quot;
<strong>Explanation:</strong> The parser will replace the &amp;amp; entity by &amp;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> text = &quot;and I quote: &amp;quot;...&amp;quot;&quot;
<strong>Output:</strong> &quot;and I quote: \&quot;...\&quot;&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= text.length &lt;= 10<sup>5</sup></code></li>
	<li>The string may contain any possible characters out of all the 256 ASCII characters.</li>
</ul>

class Solution {
public:
    string entityParser(string text) {
        int n = text.size();
        int i = 0;
        string ret = "";
        ret.reserve(n);
        while(i < n){
            while(i < n && text[i] != '&'){
                ret.push_back(text[i]);
                i++;
            }
            if(i == n) continue;
            if(i >= n-3){
                ret.push_back('&');
                i++;
                continue;
            }
            string ss4 = text.substr(i, 4);
            if(ss4 == "&gt;"){
                ret.push_back('>');
                i += 4;
                continue;
            } else if(ss4 == "&lt;"){
                ret.push_back('<');
                i += 4;
                continue;
            }
            if(i == n-4){
                ret.push_back('&');
                i++;
                continue;
            }
            if(text.substr(i, 5) == "&amp;"){
                ret.push_back('&');
                i += 5;
                continue;
            }
            if(i == n-5){
                ret.push_back('&');
                i++;
                continue;
            }
            string ss6 = text.substr(i, 6);
            if(ss6 == "&quot;"){
                ret.push_back('"');
                i += 6;
                continue;
            } else if(ss6 == "&apos;"){
                ret.push_back('\'');
                i += 6;
                continue;
            }
            if(i == n-6){
                ret.push_back('&');
                i++;
                continue;
            }
            if(text.substr(i, 7) == "&frasl;"){
                ret.push_back('/');
                i += 7;
                continue;
            }
            ret.push_back('&');
            i++;
        }
        return ret;
    }
};
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