Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where:

'.' Matches any single character.

'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

Example 1:

Input: s = "aa", p = "a"

Output: false

Explanation: "a" does not match the entire string "aa".

Example 2:

Input: s = "aa", p = "a*"

Output: true

Explanation: '*' means zero or more of the preceding element, 'a'. Therefore, by repeating 'a' once, it becomes "aa".

Example 3:

Input: s = "ab", p = ".*"
Output: true
Explanation: ".*" means "zero or more (*) of any character (.)".

Constraints:

1 <= s.length <= 20

1 <= p.length <= 30

s contains only lowercase English letters.

p contains only lowercase English letters, '.', and '*'.
It is guaranteed for each appearance of the character '*', there will be a previous valid character to match.

**Code : - **

def isMatch(self, s: str, p: str) -> bool:

return self.isMat(s, p, len(s)-1, len(p)-1, False)

```
def isMat(self, s: str, p: str, si: int, pi: int, isAst):
if pi < 0:
return si < 0
if p[pi] == '*':
return self.isMat(s, p, si, pi-1, True)
result = False
if isAst:
if si >= 0 and self.compare(s[si], p[pi]):
result = result or self.isMat(s, p, si-1, pi, True)
result = result or self.isMat(s, p, si, pi-1, False)
elif si >= 0 and self.compare(s[si], p[pi]):
result = result or self.isMat(s, p, si-1, pi-1, False)
return result
def compare(self, a, b):
return a == b or a == '.' or b == '.'
```

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