Find the Factorial of the Number using Recursion in Python

October 14, 2022

Factorial of a Number using Recursion in Python

Here, on this page, we will learn how to find the Factorial of a Number using Recursion in Python programming language. We will discuss various methods to solve the given problem.

Factorial of a Number using Recursion

Method Discussed :

  • Method 1 : Using Recursion
  • Method 2 : Using Iteration.

Algorithm ( Method 1 )

  • Call function getFactorial(num)
  • Set base case when num== 0 return 1
  • Other cases return num * getFactorial(num-1);

Time and Space Complexity :

  • Time complexity: O(N)
  • Space complexity: O(1)
  • Auxiliary Space complexity (Function call stack): O(N)
Factorial of a Number using Recursion in Python

Python Code

Run 
def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n - 1)


num = 5
print("Factorial of", num, "is", factorial(num))

Output

Factorial of 5 is 120

Algorithm ( Method 2 )

  • Initialize fact = 1
  • If num < 0 : Print Error as we can’t calculate factorial of a negative number
  • Else run an iterative loop in the iteration of (i) between [1, num]
  • Set fact = fact * i
  • Print the value of the fact.

Time and Space Complexity :

  • Time complexity: O(N)
  • Space complexity: O(1)
Run 
def factorial(n):
    res = 1
    for i in range(2, n + 1):
        res *= i
    return res


num = 5
print("Factorial of", num, "is", factorial(num))

Output

Factorial of 5 is 120

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