Leetcode•Aug 09, 2025
Regular Expression Matching
Hazrat Ali
Leetcode
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 (.)".
Solution
/**
*
* @param {string} s
* @param {string} p
* @return {boolean}
*/
const isMatch = (s, p) => {
if (p.length === 0) {
return s.length === 0;
}
const isFirstMatch = s.length > 0 && (s[0] === p[0] || p[0] === '.');
if (p.length >= 2 && p[1] === '*') {
return isMatch(s, p.substring(2)) || (isFirstMatch && isMatch(s.substring(1), p));
} else {
return isFirstMatch && isMatch(s.substring(1), p.substring(1));
}
};