So I need to reverse a Linked List in O(N) time/space.
This implementation is what I came up with using only the LinkedList class in the Java standard library (which doesn’t give me access to the nodes themselves).
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So I need to reverse a Linked List in O(N) time/space.
This implementation is what I came up with using only the LinkedList class in the Java standard library (which doesn’t give me access to the nodes themselves).
No, it’s not.
input.get(idx);is itselfO(idx)in time, which makes your implementation quadratic in time.You will probably want to use an iterator (or better yet
listIterator).EDIT: Also, you could easily eliminate holdPopped with a little rearrangement.
holdPopped.addwill be trivially O(1) in both time and space since you’re pre-allocating space (which is O(n) in space) by passing the size.IIRC,
holdLL.addis amortized O(1) in time and space as well. Sometimes it will be more, sometimes less, but the total space is n, so it should average to to O(n). You can simplify the analysis by usingholdLL.ensureCapacity.