Lists represent a sequential ordering of elements. Maps are used to represent a collection of key / value pairs. While you could use a map as a list, there are some definite downsides of doing so. Maintaining order: A list by definition is ordered. You add items and then you are able to iterate back … Read more
There’s code in one reply that spells it out, but you might find it easier to start from the bottom up, by asking and answering tiny questions (this is the approach in The Little Lisper): What is the reverse of null (the empty list)? null. What is the reverse of a one element list? the … Read more
It is reasonable to expect that you cannot do any better than O(N log N) in running time. However, the interesting part is to investigate whether you can sort it in-place, stably, its worst-case behavior and so on. Simon Tatham, of Putty fame, explains how to sort a linked list with merge sort. He concludes … Read more
The following is by far the greatest of all I have seen – O(N), no counters. I got it during an interview to a candidate S.N. at VisionMap. Make an interating pointer like this: it goes forward every time till the end, and then jumps to the beginning of the opposite list, and so on. … Read more
Any alternative? No, this is as simple as it gets, and there’s no fundamentally-different way of doing it. This algorithm is already O(n) time, and you can’t get any faster than that, as you must modify every node. It looks like your code is on the right track, but it’s not quite working in the … Read more
It’s not just better, it’s the only possible way. If you stored a Node object inside itself, what would sizeof(Node) be? It would be sizeof(int) + sizeof(Node), which would be equal to sizeof(int) + (sizeof(int) + sizeof(Node)), which would be equal to sizeof(int) + (sizeof(int) + (sizeof(int) + sizeof(Node))), etc. to infinity. An object like … Read more
Linked lists are very useful when you need to do a lot of insertions and removals, but not too much searching, on a list of arbitrary (unknown at compile-time) length. Splitting and joining (bidirectionally-linked) lists is very efficient. You can also combine linked lists – e.g. tree structures can be implemented as “vertical” linked lists … Read more
The obvious solution to developers familiar to Java is to use the LinkedList class already provided in java.util. Say, however, you wanted to make your own implementation for some reason. Here is a quick example of a linked list that inserts a new link at the beginning of the list, deletes from the beginning of … Read more
You are correct, the article considers “Indexing” as a separate operation. So insertion is itself O(1), but getting to that middle node is O(n).
For some needs, a deque may also be useful. You can add and remove items on both ends of a deque at O(1) cost. from collections import deque d = deque([1,2,3,4]) print d for x in d: print x print d.pop(), d