private Node start;

private Node end;

public NodeIterator(List<Integer> values) {

Node prev = null;

for (Integer value : values) {

var current = new Node(value);

if (start == null) {

start = current;

end = current;

current.setPrev(null);

} else {

end = current;

current.setPrev(prev);

}

prev = current;

}

}

// 1 -> 2 -> 3 -> 7 -> 9 -> 11 = Output: 12,11,10

// 1 -> 2 -> 3 -> 7 -> 9 = Output: 12,11,3

// Start -> End ->

public void calculateSumEdge() {

System.out.println("---------------");

var currentI = start;

var currentJ = end;

while (currentI != null && currentJ != null && currentI != currentJ && currentI.getPrev() != currentJ) {

System.out.println(currentI.getData() + currentJ.getData());

// Move forward

currentI = currentI.getNext();

// Move backward

currentJ = currentJ.getPrev();

}

// If pointers meet in the middle, print the middle node's data

if (currentI == currentJ) {

System.out.println(currentI.getData());

}

System.out.println("---------------");

}

public static void main(String[] args) {

var listValues = new LinkedList<Integer>();

listValues.add(1);

listValues.add(2);

listValues.add(3);

listValues.add(4);

listValues.add(7);

listValues.add(9);

listValues.add(11);

var iterator = new NodeIterator(listValues);

iterator.calculateSumEdge();

}

public static class Node {

private NodeIterator.Node prev;

private final int data;

private NodeIterator.Node next;

public Node(int data) {

this.data = data;

}

public NodeIterator.Node getPrev() {

return prev;

}

public void setPrev(NodeIterator.Node prev) {

this.prev = prev;

if (this.prev != null) {

this.prev.setNext(this);

}

}

public int getData() {

return data;

}

public NodeIterator.Node getNext() {

return next;

}

public void setNext(NodeIterator.Node next) {

this.next = next;

}

}