Choosing the base case

See how 0! = 1 base case works and the danger of a wrong one.

Base case selection

Factorial's base case is 0! = 1. This stops the recursion. A wrong base case causes infinite calls.

1! = 1 can also be used as a base case. Then the recursive step starts from 1 and one call is saved.

Recursive factorial's complexity is O(n): each call decreases n by one, totaling n calls. Unlike Fibonacci, there is no repetition.

Memory complexity is also O(n) because each call adds a frame to the stack. The iterative solution uses O(1) memory.

Write factorial_call(n). If n=1 return 1, else n * factorial_call(n-1). Print 24 with print(factorial_call(4)).

Show example solution

def factorial_call(n):
    # Call factorial
    if n == 1:
        return 1
    return n * factorial_call(n - 1)
print(factorial_call(4))

Memory complexity

Recursive factorial memory complexity is ____.

Show answer

Recursive factorial memory complexity is O(n).