> For the complete documentation index, see [llms.txt](https://blog.bernardw.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://blog.bernardw.com/problems/regular-expression-matching.md).

# 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
```

{% tabs %}
{% tab title="Scala" %}

```scala
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")
```

{% endtab %}

{% tab title="Second Tab" %}

{% endtab %}
{% endtabs %}