Regular Expression Matching

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).

The function prototype should be: bool isMatch(const char *s, const char *p)

Some examples:

isMatch("aa","a") → false
isMatch("aa","aa") → true
isMatch("aaa","aa") → false
isMatch("aa", "a*") → true
isMatch("aa", ".*") → true
isMatch("ab", ".*") → true
isMatch("aab", "c*a*b") → true
def isMatch(s: String, p: String): Boolean = {
  if (s.isEmpty) true
  else if (p.isEmpty) false
  else if (p.length >= 2 && p(1) == '*') {
    if (p.head == '.' || s.head == p.head) {
      isMatch(s.tail, p.substring(2)) || isMatch(s.tail, p)
    }
    else isMatch(s, p.substring(2))
  }
  else {
    if (p.head == '.' || s.head == p.head) {
      isMatch(s.tail, p.tail)
    }
    else false
  }
}

isMatch("aa", "a")
isMatch("aa", "aa")
isMatch("aaa", "aa")
isMatch("aa", "a*")
isMatch("aa", ".*")
isMatch("ab", ".*")
isMatch("aab", "c*a*b")