10 Regular Expression Matching

 Given an input string (s) and a pattern (p), implement regular expression matching with support for '.' and '*'.

'.' Matches any single character.
'*' Matches zero or more of the preceding element.
The matching should cover the entire input string (not partial).

Note:

s could be empty and contains only lowercase letters a-z.
p could be empty and contains only lowercase letters a-z, and characters like . or *.
Example 1:

Input:
s = "aa"
p = "a"
Output: false
Explanation: "a" does not match the entire string "aa".
 
 
 public boolean isMatch(String s, String p) {
        
        boolean[][] dp = new boolean[s.length()+1][p.length()+1];
        dp[0][0] = true;
        
        char[] string = new char[s.length()+1];
        char[] pattern = new char[p.length()+1];
        
        string[0] = (char)0;
        pattern[0] = (char)0;
        
        for(int i=0;i<s.length();i++){
            string[i+1] = s.charAt(i);
        }
        
        for(int i=0;i<p.length();i++){
            pattern[i+1] = p.charAt(i);
        }
        
        for(int i=1;i<pattern.length;i++){
            if(pattern[i]=='*' && dp[0][i-2]==true){
                dp[0][i] = true;
            }
        }
        
        for(int i=1;i<string.length;i++){
            for(int j=1;j<pattern.length;j++){
                if(pattern[j]==string[i] || pattern[j]=='.'){
                    dp[i][j] = dp[i-1][j-1];
                }else if(pattern[j]=='*'){
                    if(pattern[j-1]==string[i] || pattern[j-1]=='.'){ 
                        dp[i][j] = dp[i][j-2] || dp[i-1][j];
                    }else{
                        dp[i][j] = dp[i][j-2];
                    }
                }
            }
        }
        
        return dp[s.length()][p.length()];

    }