10. Regular Expression Matching

class Solution {
    public boolean isMatch(String s, String p) {
        return isMatch(s, 0, p, 0);
    }
    public boolean isMatch(String s, int i, String p, int j) {
        if(i==s.length()&&j==p.length())
            return true;
        if(i>s.length()||j>=p.length())
            return false;
        if(j+1<p.length()&&p.charAt(j+1)==‘*‘)
        {
            boolean ret=isMatch(s,i,p,j+2);
            if(i<s.length()&&(p.charAt(j)==‘.‘||s.charAt(i)==p.charAt(j)))
                ret=ret||isMatch(s,i+1,p,j);
            return ret;
        }
        if(i<s.length()&&(p.charAt(j)==‘.‘||s.charAt(i)==p.charAt(j)))
            return isMatch(s,i+1,p,j+1);
        return false;
    }
}

//isMatch(p,i,s,j)
//if(p[i]==s[j]||p[i]==‘.‘) isMatch(p,i-1,s,j-1)
//if(p[i]==‘*‘) isMatch(p,i-2,s,j)
//if(p[i]==‘*‘&&(p[i-1]==s[j]||p[i-1]==‘.‘) isMatch(p,i-1,s,j)||isMatch(p,i,s,j-1)
class Solution {
    public boolean isMatch(String s, String p) {
        boolean[][] dp=new boolean[p.length()+1][s.length()+1];
        dp[0][0]=true;
        for(int i=1;i<=p.length();i++)
            for(int j=0;j<=s.length();j++)
                dp[i][j]=j>0&&(p.charAt(i-1)==s.charAt(j-1)||p.charAt(i-1)==‘.‘)&&dp[i-1][j-1]
                ||p.charAt(i-1)==‘*‘&&i>1&&dp[i-2][j]
                ||p.charAt(i-1)==‘*‘&&i>1&&j>0&&(p.charAt(i-2)==s.charAt(j-1)||p.charAt(i-2)==‘.‘)&&(dp[i-1][j]||dp[i][j-1]);
        return dp[p.length()][s.length()];
    }
}