Regular expression matching

src/main/java/com/thealgorithms/Recursion/RegexMatchingRecursive.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.Recursion;
+
+// For explanation of problem statement, please paste the following URL : https://www.geeksforgeeks.org/implementing-regular-expression-matching/
+
+public class RegexMatchingRecursive {
+    public boolean isMatch(String s, String p) {
+        // Base case: Return is p is empty
+        if (p.isEmpty()) {
+            return s.isEmpty();
+        }
+
+        // Check if the first character of s matches the first character of p.
+        boolean firstMatch = !s.isEmpty() && p.charAt(0) == s.charAt(0) || p.charAt(0) == '.';
+
+        // So...If there's a '*' in the second position of p i.e., p.charAt(1) == '*'
+        // it means we can either:
+        // 1. Ignore the '*' and the preceding character (move to p.substring(2)).
+        // 2. Use the '*' to match the first character of s if there's a match.
+
+        if (p.length() >= 2 && p.charAt(1) == '*') {
+            return isMatch(s, p.substring(2)) || (firstMatch && isMatch(s.substring(1), p));
+        } else {
+            // Otherwise, check the next characters of both s and p.
+            return firstMatch && isMatch(s.substring(1), p.substring(1));
+        }
+    }
+
+    public static void main(String[] args) {
+        RegexMatchingRecursive solution = new RegexMatchingRecursive();
+
+        // Test cases
+        System.out.println(solution.isMatch("aab", "c*a*b")); // Output: true
+        System.out.println(solution.isMatch("mississippi", "mis*is*p*.")); // Output: false
+    }
+}