需求

2.代码

    public class RegularExpressionMatching {
        public boolean isMatch(String s, String p) {
            if (p.isEmpty()) {
                return s.isEmpty();
            }

            boolean firstMatch =!s.isEmpty() && (s.charAt(0) == p.charAt(0) || p.charAt(0) == '.');

            if (p.length() >= 2 && p.charAt(1) == '*') {
                return isMatch(s, p.substring(2)) || (firstMatch && isMatch(s.substring(1), p));
            } else {
                return firstMatch && isMatch(s.substring(1), p.substring(1));
            }
        }

        public static void main(String[] args) {
            RegularExpressionMatching rem = new RegularExpressionMatching();
            String s = "aa";
            String p = "a";
            System.out.println(rem.isMatch(s, p)); // false

            s = "aa";
            p = "a*";
            System.out.println(rem.isMatch(s, p)); // true

            s = "ab";
            p = ".*";
            System.out.println(rem.isMatch(s, p)); // true
        }
    }