*10. Regular Expression Matching

1. "p"的第一个字符为"*"；
2. 边缘条件，s 或者 p 为空；
3. 填充table。p=="*"(either 0 or match 1, match more than one can be reduced to match 1)； p != "*"；

public class Solution {
    public boolean isMatch(String s, String p) {
        if(p.charAt(0)=='*')    return false;
        boolean M[][] = new boolean[s.length()+1][p.length()+1];
        // s is empty:
        M[0][0] = true;
        for(int j=1; j<=p.length(); j++) {
            M[0][j] = p.charAt(j-1)=='*' && M[0][j-2];
        }
        // p is empty:
        for(int i=1; i<=s.length(); i++) {
            M[i][0] = false;
        }
        // fill the table:
        for(int i=1; i<=s.length(); i++) {
            for(int j=1; j<=p.length(); j++) {
                if(p.charAt(j-1) != '*') {
                    M[i][j] = ((p.charAt(j-1) == s.charAt(i-1)) || (p.charAt(j-1) == '.')) && M[i-1][j-1];
                } else {
                    M[i][j] = M[i][j-2] || ((p.charAt(j-2)==s.charAt(i-1) || p.charAt(j-2)=='.') && M[i-1][j]);
                }
            }
        }
        return M[s.length()][p.length()];
    }
}