public class regularExpressionMatching {
    /* 深夜思考，这里有四种state equation情况，是否可以说成 rule 1, rule 2. 然后举例的时候可以引用
    * */
    /*
    1, If p.charAt(j) == s.charAt(i) :  dp[i][j] = dp[i-1][j-1];
    2, If p.charAt(j) == '.' : dp[i][j] = dp[i-1][j-1];
    3, If p.charAt(j) == '*':
    here are two sub conditions:
               1   if p.charAt(j-1) != s.charAt(i) : dp[i][j] = dp[i][j-2]  //in this case, a* only counts as empty
               2   if p.charAt(j-1) == s.charAt(i) or p.charAt(j-1) == '.':
                              dp[i][j] = dp[i-1][j]    //in this case, a* counts as multiple a
                           or dp[i][j] = dp[i][j-1]   // in this case, a* counts as single a
                           or dp[i][j] = dp[i][j-2]   // in this case, a* counts as empty
    * */
    public static void main(String[] args){
        String s = "dabdokdfa";
        // 忽然发现 ".*" 无敌了
        String p = ".*";
        System.out.println(isMatch(s,p));
    }
    public static boolean isMatch(String s, String p) {

        if (s == null || p == null) {
            return false;
        }
        boolean[][] dp = new boolean[s.length()+1][p.length()+1];
        dp[0][0] = true;
        for (int i = 0; i < p.length(); i++) {
            if (p.charAt(i) == '*' && dp[0][i-1]) {
                dp[0][i+1] = true;
            }
        }
        for (int i = 0 ; i < s.length(); i++) {
            for (int j = 0; j < p.length(); j++) {
                if (p.charAt(j) == '.') {
                    dp[i+1][j+1] = dp[i][j];
                }
                if (p.charAt(j) == s.charAt(i)) {
                    dp[i+1][j+1] = dp[i][j];
                }
                if (p.charAt(j) == '*') {
                    if (p.charAt(j-1) != s.charAt(i) && p.charAt(j-1) != '.') {
                        dp[i+1][j+1] = dp[i+1][j-1];
                    } else {
                        dp[i+1][j+1] = (dp[i+1][j] || dp[i][j+1] || dp[i+1][j-1]);
                    }
                }
            }
        }
        return dp[s.length()][p.length()];
    }
}