Python Coding challenge - Day 293| What is the output of the following Python Code?

 

Code Explanation:

def recursive_sum(n):

This defines a function named recursive_sum that takes one argument n.

The function is designed to calculate the sum of all integers from n down to 0 using recursion.

 if n == 0:

This checks whether n is equal to 0.

This is the base case of the recursive function. A base case is a condition where the recursion stops. Without it, the function would call itself indefinitely, causing a stack overflow error.

return 0

If the condition n == 0 is true, the function returns 0.

This is the terminating condition of the recursion, ensuring that the function doesn't call itself further when n reaches 0.

return n + recursive_sum(n - 1)

If n is not 0, this line gets executed.

It does two things:

Adds the current value of n to the result of the function call recursive_sum(n - 1).

Calls recursive_sum with a smaller value (n - 1), which moves closer to the base case.

This is the recursive step where the function breaks the problem into smaller sub-problems.

print(recursive_sum(4))

This calls the recursive_sum function with the argument 4.

The function starts the recursive process and ultimately prints the final result after all recursive calls complete.

Step-by-Step Execution

Let’s see how the function runs when n = 4:

1st Call:

n = 4

The condition if n == 0 is false.

The function returns:

4 + recursive_sum(3)

2nd Call:

n = 3

The condition if n == 0 is false.

The function returns:

3 + recursive_sum(2)

3rd Call:

n = 2

The condition if n == 0 is false.

The function returns:

2 + recursive_sum(1)

4th Call:

n = 1

The condition if n == 0 is false.

The function returns:

1 + recursive_sum(0)

5th Call (Base Case):

n = 0

The condition if n == 0 is true.

The function returns 0.

Returning Results

Now, the results are returned step by step:

recursive_sum(0) returns 0.

recursive_sum(1) returns 1 + 0 = 1.

recursive_sum(2) returns 2 + 1 = 3.

recursive_sum(3) returns 3 + 3 = 6.

recursive_sum(4) returns 4 + 6 = 10.

Final Output:

10