regular-expression-matching

string/regular-expression-matching.js

@@ -0,0 +1,53 @@
+/**
+10. Regular Expression Matching
+
+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 <= 20
+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.
+*/
+
+/**
+ * @param {string} s
+ * @param {string} p
+ * @return {boolean}
+ */
+var isMatch = function (s, p) {
+  if (p.length === 0) {
+    return s.length === 0;
+  }
+
+  const isFirstMatched = s.length > 0 && (s[0] === p[0] || p[0] === ".");
+
+  if (p.length >= 2 && p[1] === "*") {
+    return (
+      isMatch(s, p.substring(2)) ||
+      (isFirstMatched && isMatch(s.substring(1), p))
+    );
+  } else {
+    return isFirstMatched && isMatch(s.substring(1), p.substring(1));
+  }
+};