leetCode - Regular Expression Matching

문제

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 (.)".

Example 4:

Input: s = "aab", p = "c*a*b" Output: true Explanation: c can be repeated 0 times, a can be repeated 1 time. Therefore, it matches "aab".

Example 5:

Input: s = "mississippi", p = "mis*is*p*." Output: false

 

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.

 

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풀이

const isMatch = function (s, p) {
    if (p.length === 0) {
        return s.length === 0;
    }

    let firstCheck = s.length > 0 && (s[0] === p[0] || p[0] === '.');
    if (p.length >= 2 && p[1] === '*') {
        return isMatch(s, p.substring(2)) || (firstCheck && isMatch(s.substring(1), p));
    } else {
        return firstCheck && isMatch(s.substring(1), p.substring(1));
    }

};