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Recursion In Python

Can someone please explain why the following code prints 300 instead of 203 def f(n): if n == 0: return 0 else: return f(n - 1) + 100 print(f(3))

1st Jun 2023, 5:01 PM
DevAbdul
DevAbdul - avatar
5 Answers
+ 4
Hi, again, Abdulrahim Jamil ! But it’s recursion. Every value f(n) is built on previouse values f(n-1), in that way it’s showed below. So f(0) -> f(1), f(1) -> f(2), …, f(n-1) -> f(n): f(0) = 0 f(1) = f(0) + 100 = 100 f(2) = ff1) + 100 = 100 + 100 = 200 f(3) = f(2) + 100 = 200 + 100 = 300
1st Jun 2023, 5:41 PM
Per Bratthammar
Per Bratthammar - avatar
+ 3
Hi, Abdulrahim Jamil ! Why should it be 203! It’s start with 0, and add 100 every time you ingrease n with 1 f(0) = 0 f(1) = 0 + 100 f(2) = 0 + 100 + 100 f(3) = 0 = 100 + 100 + 100
1st Jun 2023, 5:18 PM
Per Bratthammar
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+ 3
Per Bratthammar thanks for clarifying that, now I remember that the function stack also works like a normal stack i.e it uses the LIFO technique, I now understand how it works. I had initially thought it would work like this: f(0) = 0 f(1) = 0 + 100 f(2) = 1 + 100 f(3) = 2 + 100 I now see why it couldn't have worked that way and I think it's because it return statement wasn't written like this: return n + f(n - 1) + 100 As you would have done when calculating the sum of numbers below a number n (without the 100 of course!). Thanks again Per Bratthammar.
1st Jun 2023, 6:26 PM
DevAbdul
DevAbdul - avatar
+ 1
Per Bratthammar it doesn't start with zero, it starts with a 3
1st Jun 2023, 5:21 PM
DevAbdul
DevAbdul - avatar
0
Mirielle I totally agree with you, as I mentioned in my reply to Per Bratthammar I approached it the same way I would a function calculating the sum of all numbers below a certain number n. Thanks
1st Jun 2023, 6:28 PM
DevAbdul
DevAbdul - avatar