chore(Python) : add GCD using recursion following Euclid's Algorithm (#797)

algorithms/Python/README.md

@@ -26,6 +26,7 @@
 - [n-th Fibonacci number](recursion/nth_fibonacci_number.py)
 - [Recursive Insertion Sort](recursion/recursive_insertion_sort.py)
 - [Recursive Sum of n numbers](recursion/recursive-sum-of-n-numbers.py)
+- [GCD by Euclid's Algorithm](recursion/gcd_using_recursion.py)
 
 
 ## Scheduling

algorithms/Python/recursion/gcd_using_recursion.py

@@ -0,0 +1,23 @@
+#EUCLIDS ALGORITHM 
+
+def gcd(a, b):
+	if a<0:
+		a = -a  
+	if b<0:
+		b = -b
+	if b==0:
+		return a  
+	else:
+		return gcd(b, a%b)
+
+
+#TIME COMPLEXITY - O(log(min(a, b)))
+#EXAMPLES
+#print(gcd(10, 2)) -> 2
+#print(gcd(30, 15)) -> 3
+#print(gcd(-30, 15)) -> 3
+#WORKING
+#We are using the Euclidean Algorithm to calculate the GCD of a number
+#it states that if a and b are two positive integers then GCD or greatest common
+#divisors of these two numbers will be equal to the GCD of b and a%b or
+#gcd(a, b) = gcd(b, a%b) till b reaches 0