adding factorial

dynamic_programming/factorial.py

@@ -0,0 +1,19 @@
+#Factorial of a number using memoization
+def factorial(num):
+    if num<0:
+        return -1
+    if result[num]!=-1:
+        return result[num]
+    else:
+        result[num]=num*factorial(num-1)
+        #uncomment the following to see how recalculations are avoided
+        #print(result)
+        return result[num]
+
+#factorial of num
+result=[-1]*10
+result[0]=result[1]=1
+print(factorial(5))
+#uncomment the following to see how recalculations are avoided
+# print(factorial(3))
+# print(factorial(7))