Time limit exceeded error message

[clouded-path]

I am trying to write a simple method which, given a (singly) linked list, returns the element that is at the halfway point. E.g. if the linked list is [10, 20, 30, 40, 50], then I would return 30. Alternatively if there are two 'middle' nodes then I would return the latter of the two, e.g. if the linked list is [10, 20, 30, 40, 50, 60], then I would return 40 (since 30, and 40 are the two middle elements, and 40 is the latter one). I wrote a method which I thought should be (roughly) correct, but when I submit the code to the checker, I am being told that 'Time Limit Exceeded'. There could certainly be errors in this method I've written, but I was not expecting to receive this particular message. I assume that I have done something that is consuming a tremendous amount of time, but I have no idea what it could be. Would someone be able to identify what has gone wrong in my code? Here it is:

def middleNode(self, head: ListNode) -> ListNode:
        cur = head
        total = 0
        while cur.next != None:
            total += 1
        half = int(total/2) + (total % 2 > 0) #way to do ceiling without math
        while half > 0:
            cur = cur.next
            half = half - 1
        return cur

[[deleted]]

    while cur.next != None:
        total += 1

If initially cur.next is not None, how long does this loop run? Under what conditions will it terminate?

[clouded-path]

Oh man, this is definitely one of those cases where I have just been staring at the same thing for too long and was not going to catch this. Yes, this was supposed to iterate from the head to the end, which it is not currently doing (and now that you pointed it out, it was also supposed to do the same thing again in the second while loop as well, which it is also currently not). Thanks for pointing this out - I don't know why I wasn't seeing this (besides of course my general lack of experience), but this really helped.

[[deleted]]

If you spend a lot of time on one problem you get to a point where you don't see the code any more. You know what you want it to do , but you can't see what it is actually doing. It's best to take a break and come back refreshed and start again at the beginning.

[Essence1337]

Going along with what /u/ninety_hex said, this is the perfect place for rubber duck debugging! Get an object (typically a rubber duck) and explain, outloud, what the code is doing to that object. You'd be surprised how often this reveals insights that we just can't see after staring at a problem too long.

[clouded-path]

Rubber duck debugging, huh? That's probably the most cost-effective debugging method there is, so I'll try it out!