Linked List with fast node order querying

问题

We are using a Doubly Linked List data structure to store some unordered data (The data as such is unordered, however the node order in the link list is relevant). A common operation on this data structure is NodeBeforeNode(Node N1, Node N2), which is given two node pointers in the list and determines which of them precedes the other.

This operation takes linear time as it needs to traverse the list to find the other element, which is pretty slow. To speed this up we have cached the ordinal number of each node within the node itself, and refreshed this cache as required. However, refreshing the cache is linear, and operations which alternatively modify the list and access this cache tend to be very slow.

I am looking for suggestions to speed up this behavior. I basically need a data structure which allows all the following operations in constant or logarithmic time:

Insertion (after or before a node)
Deletion of a node
NodeBeforeNode

Can anyone suggest a linked-list like structure which supports the same?

Thanks!

回答1:

Implement a modified Binary search tree,

struct node {
   /*add your data*/
   node *parent;
   node *left;
   node *right;
}

in which you can access the previous element via a parent pointer and Insertion, searching and deletion time is in O(logn)

回答2:

Maybe you should consider updating nodes with some kind of index? Insertion and deletion of node is for sure clue, that list should be the linkedlist implementation. I suggest adding new variable into node representing its position in list.

So basically:

every new item inserted into end should have index=last_index+CONST
every new item inserted into list should have index=arithmetic mean of neighbours

This of course works only if given two nodes are on the same list. Comparing them would be simple index comparing.

Please notice, that index should be floating point number. This simple scenario assumes, that there are infinitely dividable. If your program would be running long time, maybe some periodic worker which multiplies indexes values should be run?

来源：https://stackoverflow.com/questions/7280301/linked-list-with-fast-node-order-querying

标签

indexing

linked-list