Member Avatar for Gaiety

hi,
i have seen somany people asking about fnding loops in a single linked list.
i would like to know is there any advantange or necessity for having loops in a linked lists.
is there any application that really requires loops in lists.

Thanks,
Gaiety

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Short answer: loops in a singly linked list are often intentional (the circular list/ring pattern) and are useful; accidental internal cycles are usually bugs. As asked, several posters here already flagged the usual detection concerns (, ) and the common intentional use (circular queues, noted by and ). The circular pattern shows up in real systems because it models rotation naturally and removes null-end checks. (kernel.org)

Concrete, practical uses where a looped list (or ring) is the right fit:

  • run/worker queues and round‑robin schedulers (cyclic servicing),
  • timer wheels / hashed wheel timers for large numbers of timeouts,
  • free‑lists and some memory allocator internals where blocks are chained in rings.
    These use-cases benefit from constant-time rotation and cheap insertion/removal at known points. (en.wikipedia.org)

Trade-offs and safe practices to avoid the “infinite loop / leak” traps:

  • make the cyclic invariant explicit: store a size or use a sentinel (dummy) node so traversal has a clear stop condition. ()
  • when using reference‑counted owners (C++ shared_ptr), cycles cause leaks; break ownership with weak_ptr or use a tracing GC. (en.cppreference.com)
  • catch pointer-corruption and use-after-free bugs with sanitizers and memory checkers (AddressSanitizer, Valgrind) during development. (clang.llvm.org)

Guideline summary: prefer a simple circular buffer (array ring) for bounded FIFOs (faster, simpler); choose a circular linked list when frequent O(1) rotations or list splice semantics are needed; document the invariant (tail vs head semantics), keep a length counter, and add unit tests that bound traversals by that length. Mentioned forum points about detection and GC are valid — treat internal cycles as either a deliberate design choice or a bug, and design APIs so the distinction is unmistakable. (en.wikipedia.org)

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Member Avatar for Member #957352

hmm.So you know how to find the loop ? Answer if floyd algorithm. And secondly, it 's appilcation is that place when you have made any searching algorthim and if it strucked in a loop, then you can use this if my searching algorithm is strucked somwehere or not. like in the graph searching. ;) thanks.

Member Avatar for Gaiety

Quoted Text Here

floyd

Member Avatar for Gaiety

Sorry, my browser is behaving strangely.

yeah i know how to detect a loop, so many links are available.
hare and tortoise,mark the node as visited. etc
do you know any other efficient way and any other problems on lists.

Member Avatar for deceptikon

i would like to know is there any advantange or necessity for having loops in a linked lists.

Well, a circular linked list is itself a loop, and they're quite useful. Internal cycles strike me more as a bug or faulty logic (hence the need for detection algorithms), but there may be niche uses that I'm not aware of.

Member Avatar for delta_frost

Yes,looped linked-list is useful in the implementation of circular queue.

Member Avatar for rubberman

Besides circular queues, looping pointer constructs are necessary to deal with when you have references to other types of items, and they may have a reference back to one of the parents in the hierarchy. There are a number of methods to detect these situations, some of which I have dealt with in the past when writing reference-counting garbage collectors for C++. One method is to use a stack and starting at the top of the list/tree and as you traverse each item, you search the stack for the next item. If found, then you have a circular (recursive) link. If not, then push the address onto the stack and continue. The cost is proportianate to the depth (complexity) of the list. I utilized some other techniques for my C++ garbage collector because I needed it to perform in a deterministic mannger for near real-time systems.

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