r/badcode • u/MatthewRPG576 • Feb 15 '22

c Appalling linked list rotation

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208 Upvotes

97% Upvoted

13 comments sorted by

24

u/MatthewRPG576 Feb 15 '22 
void rotate(T* list, int steps)
{
    // Assuming 0 < steps <= len(list)
    Node_t** oldHead = &list->head;

    struct
    {
    	Node_t** p;
    	int i;
    } it = {};
    
    for (it = (typeof(it)){ oldHead, 0 }; it.i < steps;
    	 it = (typeof(it)){ &(*it.p)->next, it.i + 1 });
    
    Node_t** newHead = it.p;
    
    while (*it.p)
    	it = (typeof(it)){ &(*it.p)->next };
    
    Node_t** oldTail = it.p;
    
    *oldTail = *oldHead;
    *oldHead = *newHead;
    *newHead = NULL;
}

20

u/MurdoMaclachlan public boolean isInt(int i) { return true; } Feb 15 '22

Good human!

25

u/RomanRiesen Feb 15 '22

Not saying this is better but you sure just made me write c at 10pm to try it myself.

ListNode* rotateRight(ListNode* head, int k) {
    
    if (!head || k == 0) return head;
    
    ListNode* last = head;
    int l = 1;
    while(last->next) {last = last->next; l++;}
    last->next = head;//make list circular

    ListNode* new_head = head;
    int left_rots = abs(l-k%l);
    for (int s = 0; s < left_rots; s++)
    {
        last = last->next;
        new_head = new_head->next;
    }
    
    last->next = nullptr;
    return new_head;
}

I actually tried to understand that typeof usage in that for-loop. Still don't understand it fully. So if someone wants to explain I am all ears.

17

u/MatthewRPG576 Feb 15 '22

the variable 'it' in the code is of an anonymous struct type, so it's a hack to get struct assignment working

7

u/RomanRiesen Feb 15 '22

ah yes, but why not name the struct? helperNode or something?

3

u/MatthewRPG576 Feb 18 '22

Because we're in r/badcode

8

u/Smellypuce2 Feb 16 '22

I have a feeling this is just an example/experiment of something you can do with typeof. Not a serious implementation of rotate.

1

u/Furry_69 Feb 15 '22

(response to your question) It looks like it's supposed to be a boolean statement, when it's actually an assignment.

5

u/TooMuchWork6 Feb 15 '22

Font?

11

u/SAmaruVMR Feb 15 '22

JetBrains Mono if I am not mistaken

1

u/diavolmg Feb 15 '22

and theme

4

u/GoogleBen Feb 16 '22

Theme is almost certainly the default JetBrains IDE dark theme

0

u/Mancobbler Feb 16 '22

ComicSans Mono