Is n power of three - Python

Question

Leet-Code 326. Power of Three: Question Link: https://leetcode.com/problems/power-of-three/description/

My Code:

 class Solution:
    def isPowerOfThree(self, n: int) -> bool:
        print(n)
        if n % 3 == 0:
            if n == 3:
                return True 
            return self.isPowerOfThree(n/3)
        else: return False

I a getting the following error. Any help!
RecursionError: maximum recursion depth exceeded while getting the str of an object

I would re-organize the code a bit with having your quick returns (n<=0, n==3 and n%3 !=0) immediately after your print statement. Also, you might avoid a recursive function. — kvantour
– kvantour, Commented Feb 10, 2023 at 16:26

Sebastian Neumann · Accepted Answer · 2023-02-10 16:25:37Z

1

Your function has no way of handling 0. If you step through the function, you print "0" (which is why it's the first thing that fails after exceeding the recursion depth), then it evaluates 0 % 3 == 0. That's True, so it goes further. 0 == 3 is False, so it returns self.isPowerOfThree(0), and you're back where you started (infinite recursion).

Hope this helped.

edited Feb 10, 2023 at 16:25

answered Feb 10, 2023 at 16:21

Sebastian Neumann

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3 Comments

Tushar Over a year ago

return (n >= 0) & ((math.log10(n)/ math.log10(3) % 1) == 0) This should have worked too, but it got a math error. Any idea? @SebastianNeumann

kvantour Over a year ago

Don't forget to check for negative numbers. Also 0 is not a power of three

slothrop Over a year ago

stackoverflow.com/questions/67645225/… - & is "bitwise and" without short-circuiting, so math.log10(n) is being evaluated even if n<0

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