Factorial using recursion cpp (#276)

Code/C++/factorial.cpp

@@ -1,33 +1,55 @@
 /*
-Factorial of a non-negative integer, is multiplication of all integers smaller than or equal to n.
+Factorial of a positive integer is the product of all integers smaller than or equal to n.
+For e.g: n!=1*2*3....*(n-1)*n
+Factorial of 0 is 1 i.e 0!=1
 */
 
 #include<iostream>
 using namespace std;
 
- int fact(int n){
+long long int factorial(int n){
  	if(n==0)
  		return 1;
- 	int ans = n*fact(n-1);
-
- 	return ans;
+ 	else if(n==1)
+ 		return 1;
+ 	else
+	{
+		long long int ans = n*factorial(n-1);
+	 	return ans;
+	}
  }
 
- int main() {
-
+int main() {
  	int n;
  	cin >> n;
- 	cout<<fact(n);
+ 	cout<<factorial(n);
  	return 0;
  }
 
 /* 
-	Test case :
+	Constraint: 0<=n<=20
 
+	Test case : 1
 	Input : 6
 	Output : 720
 
-	Time complexity: O(n)
-	Space Complexity: O(n)
+
+	Test case : 2
+	Input : 1
+	Output : 1
+
+	Test case : 3
+	Input : 0
+	Output : 1
+
+*/
+
+/*	
+	Recurrence Relation:
+	Base Case:  T(n)=1          , n=0
+				T(n)=T(n-1) + 1 , n>0
+
+	Time complexity(T(n)) : O(n)
+	Space Complexity : O(n)
 
- */
+ */