<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>

struct NFA
{
    char G[200];
    bool T[200];
    int cnt;

    void build(string p)
    {
        int i = 0;
        while (i < p.length())
        {
            char c = p[i];
            char d = p[i+1];

            if (c == '*') {i++; continue;}
            G[cnt] = c;
            T[cnt] = (d == '*');
            ++cnt;
            if (d == '*') i++;
            i++;
        }
    }

    bool match(string s)
    {
        set<int> nodes = {0};
        int i = 0;
        while (i < s.length())
        {
            set<int> next_nodes;
            bool flag = false;
            while(!nodes.empty())
            {
                int node = *nodes.begin();
                nodes.erase(nodes.begin());

                char c = s[i];
                if (G[node] != '.' && G[node] != c && !T[node]) continue;
                if ((G[node] == '.' || G[node] == c) && T[node]) {next_nodes.insert(node);};
                if ((G[node] == '.' || G[node] == c) && node+1 < cnt) {next_nodes.insert(node+1);}
                if (node+1 < cnt && T[node]) {nodes.insert(node+1);}
                if ((G[node] == '.' || G[node] == c) && node+1 == cnt) flag = true;
            }
            if (i == s.length() - 1)
            {
                if (flag) return true;
                for (int node : next_nodes)
                {
                    while(T[node]) {++node;}
                    if (node == cnt) {return true;}
                }
            }
            if (next_nodes.empty()) return false;
            nodes = next_nodes;
            i++;
        }
        return false;
    }
};

class Solution {
      
public:
    bool isMatch(string s, string p) {
        NFA nfa = {};
        nfa.build(p);
        return nfa.match(s);
    }
};
11056