Performance: Append operation of List and Array about functionaljava

[tonymorris]

snoc is O(n) for a single-linked list.

[morris821028]

@tonymorris Could it be O(log n) for a doubly-linked list? The common interface of List is often implemented by doubly-linked list for better performance.

[tonymorris]

A double-linked list has O(1) snoc but does not give better performance. It gives a trade-off. You can obtain O(1) cons and snoc with:

// see fj.data.DList
public class DList<A> {
    private final F<List<A>,List<A>> appendFn;
}

Note that head and tail are O(n). A finger-tree gives different trades again.

[morris821028]

@tonymorris Thanks your information. I forgot to study DList in this project.

In java.util, LinkedList implements Deque interface. If we consider real-time deque as DList implementation corresponding to paper REAL-TIME DEQUES, MULTIHEAD TURING MACHINES and PURELY FUNCTIONAL PROGRAMMING, Tyng-Runey Chuang and Benjamin Goldberg, 1993.

• cons and snoc: O(1)
• head and tail: O(1)
• append(List): O(m), which m is the number of appended elements.

I'm interested in the real cases prefer which kind of operation?

[tonymorris]

I think both are useful. Feel free to write Deque as a pair of lists.

[mperry]

Closing.