在双链表中的某个节点之前插入节点

Question

I have created Doubly Linked List as below

8 <-> 2 <-> 12

I have to insert following nodes before node "2"

Nodes to insert -(8,22,23,15)

Node "8" is already present before node "2", In this case i don't want to insert node "8" again. Is there any way to check "node to insert" is already present before the node or not?

I want final DLL as 8 <-> 22 <-> 23 <-> 15 <-> 2 <-> 12

Answer 1

However, if you don't want to repeat series:

Current List:

1 ↔ 2 ↔ 3

Insert before 3: (1, 2, 4)

Result wanted:

1 ↔ 2 ↔ 4 ↔ 3

It gets a little bit more complicated, but not much.

First , check if the node before the one you use as base matches any of your to introduce nodes. Starting for the last one (so you get always the longest series repeated, and avoid it).

If one matches check if the rest of the serie before it matches too. If it does, start from the next (or add none, if it's the last); if it doesn't, go back to First step.

Second and last After you have selected the next node to add (if you didn't match any on First , just start on the first one) just add them before the base .

This is pseudocode, since I don't know your exact implementation:

Considering:

int[] toAdd = {1, 2, 4};

For example, you can use recursivity:

main {
    int from = 0;
    for (int i = toAdd.length - 1; i >= 0; i--) {
        if (checkSerie(toAdd, i, base) {
            from = i;
            break;
        }
    }

    // And add:
    for (int i = from; i < toAdd.length; i++) {
        addBefore(3, toAdd[i]); // Your add method.
    }
}

private boolean checkSerie (int[] toAdd, int index, Node base){
    Node prev = base.prev;
    if (index < 0) {
        return true;
    }

    if (toAdd[index] != prev) {
        return false;
    }

    return checkSeriei (toAdd, index - 1, prev);
}

Note: I haven't tested this, it might be buggy (maybe some wrong -1 or stuff like that), but should be enough to help you get the idea.