From e03b20131d50ff94fa362db3e1d18ba05b50cd24 Mon Sep 17 00:00:00 2001
From: Maryam Mughal <mm2734@njit.edu>
Date: Fri, 12 Sep 2025 09:21:49 -0400
Subject: [PATCH] Add gcd_mm2734.py with recursive gcd implementation

---
 students_submissions/gcd_mm2734.py | 37 ++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 students_submissions/gcd_mm2734.py

diff --git a/students_submissions/gcd_mm2734.py b/students_submissions/gcd_mm2734.py
new file mode 100644
index 0000000..214bad3
--- /dev/null
+++ b/students_submissions/gcd_mm2734.py
@@ -0,0 +1,37 @@
+def gcd(a: int, b: int) -> int:
+    """
+    Calculate the greatest common divisor (GCD) of two integers a and b
+    using the Euclidean algorithm (recursive; no loops).
+    Returns None if input is invalid.
+    """
+
+    # Validate inputs
+    if not isinstance(a, int) or not isinstance(b, int):
+        print("Error: gcd expects two integers.")
+        return None
+
+    if a == 0 and b == 0:
+        print("Error: gcd(0, 0) is undefined.")
+        return None
+
+    # Work with absolute values so negatives don’t break logic
+    a, b = abs(a), abs(b)
+
+    # Base case
+    if b == 0:
+        return a
+
+    # Recursive step
+    return gcd(b, a % b)
+
+
+# ------------------------
+# Basic test cases
+# ------------------------
+if __name__ == "__main__":
+    print(gcd(54, 24))    # Expected output: 6
+    print(gcd(48, 18))    # Expected output: 6
+    print(gcd(101, 10))   # Expected output: 1
+    print(gcd(-42, 56))   # Expected output: 14
+    print(gcd(0, 15))     # Expected output: 15
+    print(gcd(0, 0))      # Expected output: Error + None