# Regular Expression Matching

10. 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
``````
``````public class Solution {
public boolean isMatch(String s, String p) {
if (p.length() == 0) {
return s.length() == 0;
}

if (p.length() == 1 || p.charAt(1) != '*') {
if (s.length() < 1) {
return false;
} else if (p.charAt(0) != s.charAt(0) && p.charAt(0) != '.') {
return false;
} else {
return isMatch(s.substring(1), p.substring(1));
}
} else {
if (isMatch(s, p.substring(2))) {
return true;
}

int i = 0;
while (i < s.length() && (s.charAt(i) == p.charAt(0) || p.charAt(0) == '.')) {
if (isMatch(s.substring(i + 1), p.substring(2))) {
return true;
}
i++;
}

return false;
}
}
}
``````

Hope this helps,
Michael