<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 solve(int i, int j, const std::string& s, const std::string& p) {
//     if (j < 0) return i < 0; 
//     if (i < 0) {
//         for (int k = 0; k <= j; ++k) {
//             if (p[k] != '*') return false;
//         }
//         return true;
//     }

//     if (s[i] == p[j] || p[j] == '.') {
//         return solve(i - 1, j - 1, s, p);
//     }
//     if (p[j] == '*') {
//         bool zero_occurrence = solve(i, j - 2, s, p);
//         bool one_occurrence=0;
//         if((s[i] == p[j - 1] || p[j - 1] == '.')){
//             one_occurrence = zero_occurrence || solve(i - 1, j, s, p);
//         }
//         return zero_occurrence || one_occurrence;
//     }

//     return false;
// }

bool isMatch(const std::string& s, const std::string& p) {
    int n = s.length();
    int m = p.length();
    vector<vector<int>> dp(n + 1, vector<int>(m + 1, 0));

    dp[0][0] = 1;

    for (int j = 1; j <= m; j++) {
        if (p[j - 1] == '*') {
            dp[0][j] = dp[0][j - 2];
        }
    }

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (p[j - 1] == s[i - 1] || p[j - 1] == '.') {
                dp[i][j] = dp[i - 1][j - 1];
            } 
            else if (p[j - 1] == '*') {

                dp[i][j] = dp[i][j - 2];

                if (p[j - 2] == s[i - 1] || p[j - 2] == '.') {
                    dp[i][j] = dp[i][j] || dp[i - 1][j];
                }
            } 
            else {
                dp[i][j] = 0;
            }
        }
    }
    return dp[n][m];
}
};
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