<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 {
    static inline bool ContainsOnlyS(const char* p) {
        while (true) {
            // end of string - good
            if (*p == '\0') {
                return true;
            }
            // next character is '*' (any current)  good
            if (*(p+1) == '*') {
                p += 2;
                continue;
            }
            return false;
        }
    }

    std::unordered_set<size_t> oks;

    inline bool put(const char *s, const char *p, bool ok) {
        oks.insert(
            size_t(s) xor (size_t(p) << 32)
        );
        return ok;
    }

    // return 0 - false, 1 - true, 2 - not set
    inline int already_processed(const char *s, const char *p) {
        const auto iter = oks.find(size_t(s) xor (size_t(p) << 32));
        return iter != oks.end();
    }

    bool checkIsMatch(const char *s, const char *p) {
        while (true) {
            if (*s == '\0') {
                return put(s, p, ContainsOnlyS(p));
            }
            if (*p == '\0') {
                return put(s, p, false);
            }

            if (already_processed(s, p)) {
                return false;
            }

            const bool nextIsS = *(p+1) == '*';
            if (nextIsS) {
                const char* ss = s;
                while (true) {
                    if (checkIsMatch(ss, p + 2)) {
                        return true;
                    }
                    if (*ss == '\0') {
                        break;
                    }
                    if (*ss == *p || *p == '.') {
                        ++ss;
                        continue;
                    }
                    break;
                }
                return put(s, p, false);
            } else {
                if (*s == *p || *p == '.') {
                    // ok
                    put(s, p, true);
                    ++s;
                    ++p;
                    continue;
                } else {
                    return put(s, p, false);
                }
            }
        }
    }
public:
    bool isMatch(const string& s, const string& p) {
        return checkIsMatch(s.data(), p.data());
    }
};

13118