<p>Given an input string <code>s</code>&nbsp;and a pattern <code>p</code>, implement regular expression matching with support for <code>&#39;.&#39;</code> and <code>&#39;*&#39;</code> where:</p>

<ul>
	<li><code>&#39;.&#39;</code> Matches any single character.​​​​</li>
	<li><code>&#39;*&#39;</code> Matches zero or more of the preceding element.</li>
</ul>

<p>The matching should cover the <strong>entire</strong> input string (not partial).</p>

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

<pre>
<strong>Input:</strong> s = &quot;aa&quot;, p = &quot;a&quot;
<strong>Output:</strong> false
<strong>Explanation:</strong> &quot;a&quot; does not match the entire string &quot;aa&quot;.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;aa&quot;, p = &quot;a*&quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> &#39;*&#39; means zero or more of the preceding element, &#39;a&#39;. Therefore, by repeating &#39;a&#39; once, it becomes &quot;aa&quot;.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;ab&quot;, p = &quot;.*&quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> &quot;.*&quot; means &quot;zero or more (*) of any character (.)&quot;.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length&nbsp;&lt;= 20</code></li>
	<li><code>1 &lt;= p.length&nbsp;&lt;= 20</code></li>
	<li><code>s</code> contains only lowercase English letters.</li>
	<li><code>p</code> contains only lowercase English letters, <code>&#39;.&#39;</code>, and&nbsp;<code>&#39;*&#39;</code>.</li>
	<li>It is guaranteed for each appearance of the character <code>&#39;*&#39;</code>, there will be a previous valid character to match.</li>
</ul>

class Solution {
public:

    bool isOK(const short sM, const short pM, short i, short n, string s, string p)
    {
        here:
        if (i>sM) 
        {
            if (n>pM) return true;
            for (short x = n+1; x<pM+2 ; x+=2)
            {
                if (p[x]!='*') return false;
            }
            return true;

        }

        if (n>pM) return false;

        if (p[n+1]=='*')
        {
            n+=2;
            if (p[n]==p[n-2]&&p[n+1]=='*') { goto here;};
            
            while (s[i]==p[n-2]||p[n-2]=='.')
            {
                if (isOK(sM,pM,i,n,s,p)) return true;
                ++i;
                if (i>sM) goto here;
            } 
            goto here;
        }
        
        
        if (s[i]==p[n]||p[n]=='.') if (isOK(sM,pM,i+1,n+1,s,p)) return true;
  
        return false;
    }

    bool isMatch(string s, string p)
    {
        if (isOK(s.length()-1,p.length()-1,0,0,s,p)) return true;
        else return false;
    }
};
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