<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:
    int n=0;
    int m=0;
    vector<int> cns;
    int dp[25][25];
    vector<bool> consec;
    
    bool solve(int i,int j,string s,string p){
        if(j>=m){
            return (i>=n)? true:false;
        }
        if(i>=n){
            bool isThereAnyNonStarCharAhead=false;
            for(int k=j;k<m-1;k++){
                if(p[k]!='*' && p[k+1]!='*'){
                    isThereAnyNonStarCharAhead=true;
                    break;
                }
            }
            if(isThereAnyNonStarCharAhead || p[m-1]!='*') return false;
            return true;
        } 

        if(dp[i][j]!=-1) return dp[i][j];

        if(s[i]==p[j]){
            if(j+1>=m || p[j+1]!='*'){
                return dp[i][j] = solve(i+1,j+1,s,p);
            }            
            return dp[i][j]=solve(i,j+1,s,p);
        }
        else if(p[j]=='*'){
            char lastChar=p[j-1];
            if(lastChar==s[i]){
                bool canBeDone=false;
                for(int k=cns[i];k>=0;k--){
                    canBeDone|=solve(i+k,j+1,s,p);
                    if(canBeDone) return true;
                }
            }
            else if(lastChar=='.'){
                bool canBeDone=false;
                for(int k=0;k<=n-i;k++){
                    canBeDone|=solve(i+k,j+1,s,p);
                    if(canBeDone) return true;
                }
            }
            else{
                return dp[i][j]=solve(i,j+1,s,p);
            }
        }
        else if(p[j]=='.'){
            if(j+1>=m || p[j+1]!='*'){
                return dp[i][j] = solve(i+1,j+1,s,p);
            }            
            return dp[i][j]=solve(i,j+1,s,p);
        }
        else if(s[i]!=p[j]){
            if (j+1>=m || p[j+1]!='*'){
                return false;
            }
            return dp[i][j]= solve(i,j+1,s,p);
        }       
        
        return dp[i][j]= false;
    }
    bool isMatch(string s, string p) {
        n=s.length();
        m=p.length();
        cns=vector<int>(n,1);

        memset(dp,-1,sizeof(dp));

        for(int i=n-2;i>=0;i--){
            if(s[i+1]==s[i]){
                cns[i]=cns[i+1]+1;
            }
            else{
                continue;
            }
        }

        // consec=vector<bool>(m,false);
        // for(int i=m-2;i>=0;i--){
        //     consec[i]=consec[i+1] | (p[i]!='*' && p[i+1]!='*');
        // }

        return solve(0,0,s,p);
    }
};
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