/**
* doA : implement the operation for A Pre-condition : x and y must exist the in the ListNode
* Post-condition : if x is to the right of y, move to left of y
*/
public void doA(int x, int y) {
ListNode lnY = null;
ListNode lnX = null;
// traverse the node until it reaches x, if it hits y along the way, continue
for (ListNode n = head; n != null; n = n.getNext()) {
if (n.getElement() == y) {
lnY = n;
}
if (n.getElement() == x) {
lnX = n;
// settle the chains for x
if (lnX == head && lnX == tail) { // only one node in the list
head = null;
tail = null;
}
}
if (lnX != null && lnY != null) {
// check whether x is on the left of Y
if (lnY.getPrev() == lnX) break;
// fix prev pointer
if (lnX != tail) {
lnX.getNext().setPrev(lnX.getPrev());
} else {
tail = lnX.getPrev();
tail.setNext(null);
}
// fix next pointer
if (lnX != head) {
lnX.getPrev().setNext(lnX.getNext());
} else {
head = lnX.getNext();
head.setPrev(null);
}
// insert it before y
if (lnY != head) {
lnX.setPrev(lnY.getPrev());
lnY.getPrev().setNext(lnX);
} else {
head = lnX;
head.setPrev(null);
}
lnY.setPrev(lnX);
lnX.setNext(lnY);
}
}
}
/**
* doR : implement the operation for R Pre-condition : valid x and there must be a ball labelled x
* in the list Post-condition : remove the ball labelled x
*/
public void doR(int x) {
for (ListNode n = head; n != null; n = n.getNext()) {
if (n.getElement() == x) {
// when found, remove that node
if (n == head && n == tail) { // only one node in the list
head = null;
tail = null;
}
// fix prev pointer
if (n != tail) {
n.getNext().setPrev(n.getPrev());
} else {
tail = n.getPrev();
tail.setNext(null);
}
// fix next pointer
if (n != head) {
n.getPrev().setNext(n.getNext());
} else {
head = n.getNext();
head.setPrev(null);
}
}
num_nodes--;
}
}