// Rotate the node to the left
private static StringAVLNode rotateLeft(StringAVLNode t) {
try {
if (t.getRight() == null) {
t.setRight(t.getRight().getLeft());
} else {
StringAVLNode temp = t.getRight();
StringAVLNode temp2 = t.getRight().getLeft();
temp.setLeft(t);
t.setRight(temp2);
t = temp;
}
} catch (Exception e) {
System.out.println("Failed Rotate Left");
}
return t;
}
private StringAVLNode replace(StringAVLNode t, StringAVLNode prev, StringAVLNode replacement) {
int oldBalance, newBalance;
if (replacement.getRight() == null) {
// at the node that will replace the deleted node
// move the replacement node – Recall there is no setVal
if (prev != null) {
prev.setRight(replacement.getLeft());
replacement.setLeft(t.getLeft());
replacement.setRight(t.getRight());
if (replacement.getBalance() != t.getBalance()) {
replacement.setBalance(t.getBalance());
}
}
replacement.setRight(t.getRight());
t = replacement;
} else {
// find the old balance
if (replacement.getRight() == null) {
oldBalance = 5;
} else {
oldBalance = replacement.getRight().getBalance();
}
t = replace(t, replacement, replacement.getRight());
// find the new balance
if (replacement.getRight() == null) {
newBalance = 3; // flag value
replacement.setBalance(replacement.getBalance() - 1);
} else {
newBalance = replacement.getRight().getBalance();
}
// update balance and rotate if needed
if (oldBalance != 0 && newBalance == 0) { // if height decreased, correct the balance
replacement.setBalance(replacement.getBalance() - 1);
}
if (replacement.getBalance() == -2) { // need to rotate?
// there are now actually 3 cases because replacement.getLeft.getBalance()
// could be -1, 0, or 1.
if (replacement.getLeft().getBalance() == -1) { // single rotation right
replacement = rotateRight(replacement);
replacement.setBalance(0);
replacement.getRight().setBalance(0);
prev.setRight(replacement);
} else if (replacement.getLeft().getBalance() == 0) { // single rotation right
if (replacement.getLeft().getLeft() == null && replacement.getLeft().getRight() == null) {
replacement = rotateRight(replacement);
replacement.setBalance(0);
replacement.getRight().setBalance(0);
prev.setRight(replacement);
} else {
replacement = rotateRight(replacement);
replacement.setBalance(1);
replacement.getRight().setBalance(-1);
prev.setRight(replacement);
}
} else { // replacement.getLeft().getBalance() == 1, double rotation case
// Check if it is a x insert or a y insert. Update balances accordingly.
if (replacement.getLeft().getRight().getBalance() == -1) {
replacement.setLeft(rotateLeft(replacement.getLeft()));
replacement = rotateRight(replacement);
replacement.setBalance(0);
replacement.getLeft().setBalance(0);
replacement.getRight().setBalance(1);
prev.setRight(replacement);
} else if (replacement.getLeft().getRight().getBalance() == 1) {
replacement.setLeft(rotateLeft(replacement.getLeft()));
replacement = rotateRight(replacement);
replacement.setBalance(0);
replacement.getLeft().setBalance(-1);
replacement.getRight().setBalance(0);
prev.setRight(replacement);
} else { // t.getLeft().getRight().getBalance() == 0
replacement.setLeft(rotateLeft(replacement.getLeft()));
replacement = rotateRight(replacement);
replacement.setBalance(0);
replacement.getLeft().setBalance(0);
replacement.getRight().setBalance(0);
prev.setRight(replacement);
}
}
}
}
return t;
}
private StringAVLNode delete(StringAVLNode t, String str) {
int oldBalance, newBalance;
if (t == null) { // Do nothing if it is not in the tree
} else if (str.compareToIgnoreCase(t.getItem()) < 0) { // get the old balance.
if (t.getLeft() == null) {
// still must deal with this special case in case
// the element to be deleted is not in the tree
oldBalance = 5; // flag value
} else {
oldBalance = t.getLeft().getBalance();
t.setLeft(delete(t.getLeft(), str));
}
// get the new balance
if (t.getLeft() == null) {
newBalance = 1; // flag value
if (oldBalance != 5) {
t.setBalance(t.getBalance() + 1);
}
} else {
newBalance = t.getLeft().getBalance();
}
if (oldBalance != 0 && newBalance == 0) { // did the height decrease?
// correct the balance
t.setBalance(t.getBalance() + 1);
}
if (t.getBalance() == 2) { // need to rotate?
// there are now actually 3 cases because t.getRight.getBalance()
// could be -1, 0, or 1.
if (t.getRight().getBalance() == 1) { // single rotation left
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
} else if (t.getRight().getBalance() == 0) { // single rotation left
if (t.getRight().getLeft() == null && t.getRight().getRight() == null) {
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
} else {
t = rotateLeft(t);
t.setBalance(-1);
t.getLeft().setBalance(1);
}
} else { // t.getRight().getBalance() == -1, double rotation case
if (t.getRight().getLeft().getBalance() == -1) {
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(1);
} else if (t.getRight().getLeft().getBalance() == 1) {
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(-1);
t.getRight().setBalance(0);
} else { // t.getRight().getLeft().getBalance() == 0
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(0);
}
}
}
} else if (str.compareToIgnoreCase(t.getItem()) > 0) {
if (t.getRight() == null) {
// still must deal with this special case in case
// the element to be deleted is not in the tree
oldBalance = 5; // flag value
} else {
oldBalance = t.getRight().getBalance();
t.setRight(delete(t.getRight(), str));
}
// get the new balance
if (t.getRight() == null) {
newBalance = -3; // flag value
if (oldBalance != 5) {
t.setBalance(t.getBalance() - 1);
}
} else {
newBalance = t.getRight().getBalance();
}
if (oldBalance != 0 && newBalance == 0) { // did the height decrease?
// correct the balance
t.setBalance(t.getBalance() - 1);
}
if (t.getBalance() == -2) { // need to rotate?
// there are now actually 3 cases because t.getLeft.getBalance()
// could be -1, 0, or 1.
if (t.getLeft().getBalance() == -1) { // single rotation right
t = rotateRight(t);
t.setBalance(0);
t.getRight().setBalance(0);
} else if (t.getLeft().getBalance() == 0) { // single rotation right
if (t.getLeft().getLeft() == null && t.getLeft().getRight() == null) {
t = rotateRight(t);
t.setBalance(0);
t.getRight().setBalance(0);
} else {
t = rotateRight(t);
t.setBalance(1);
t.getRight().setBalance(-1);
}
} else { // t.getLeft().getBalance() == 1, double rotation case
// Check if it is a x insert or a y insert. Update balances accordingly.
if (t.getLeft().getRight().getBalance() == -1) {
t.setLeft(rotateLeft(t.getLeft()));
t = rotateRight(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(1);
} else if (t.getLeft().getRight().getBalance() == 1) {
t.setLeft(rotateLeft(t.getLeft()));
t = rotateRight(t);
t.setBalance(0);
t.getLeft().setBalance(-1);
t.getRight().setBalance(0);
} else { // t.getLeft().getRight().getBalance() == 0
t.setLeft(rotateLeft(t.getLeft()));
t = rotateRight(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(0);
}
}
}
} else { // t is the node to be deleted
if (t.getLeft() == null) { // one of the easy cases
// Replace t with right subtree
t = t.getRight();
} else if (t.getRight() == null) { // the other easy case
// Replace t with left subtree
t = t.getLeft();
} else {
// get the old balance
// this is getLeft because we are using the inorder predecessor for replace
// nullPrev is to check for the special case when prev is null and
// update the balance of the replaced node properly.
boolean nullPrev = false;
int tBalance = 0;
if (t.getLeft() == null) {
oldBalance = 5; // flag value
} else {
oldBalance = t.getLeft().getBalance();
}
if (t.getLeft().getRight() == null) {
nullPrev = true;
tBalance = t.getBalance();
}
// find the replacement node and move it up
t = replace(t, null, t.getLeft());
// get the new balance
if (t.getLeft() == null) {
newBalance = 3; // flag value
t.setBalance(t.getBalance() + 1);
} else {
newBalance = t.getLeft().getBalance();
}
// just like before, see if height decrease and if so
// check to see if only need to change balance values or rotate
if (oldBalance != 0 && newBalance == 0) { // if height decreased, correct the balance
t.setBalance(t.getBalance() + 1);
}
if (nullPrev) {
t.setBalance(tBalance + 1);
}
if (t.getBalance() == 2) { // need to rotate?
// there are now actually 3 cases because t.getRight.getBalance()
// could be -1, 0, or 1.
if (t.getRight().getBalance() == 1) { // single rotation left
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
} else if (t.getRight().getBalance() == 0) { // single rotation left
if (t.getRight().getLeft() == null && t.getRight().getRight() == null) {
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
} else {
t = rotateLeft(t);
t.setBalance(-1);
t.getLeft().setBalance(1);
}
} else { // t.getRight().getBalance() == -1, double rotation case
if (t.getRight().getLeft().getBalance() == -1) {
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(1);
} else if (t.getRight().getLeft().getBalance() == 1) {
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(-1);
t.getRight().setBalance(0);
} else { // t.getRight().getLeft().getBalance() == 0
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(0);
}
}
}
}
}
return t;
}
private StringAVLNode insert(String str, StringAVLNode t) {
int oldBalance, newBalance;
if (t == null) { // easiest case – inserted node goes here
t = new StringAVLNode(str);
} else if (t.getItem() == str) { // already in the tree – do nothing
} else if (str.compareToIgnoreCase(t.getItem()) < 0) {
// str is smaller than this node – go left
// get the old balance of the left child (where the insertion
// is taking place)
// oldBalance is the balance of the right/left subtree
if (t.getLeft() == null) {
oldBalance = -3; // flag value
t.setBalance(t.getBalance() - 1);
} else {
oldBalance = t.getLeft().getBalance();
}
t.setLeft(insert(str, t.getLeft()));
newBalance = t.getLeft().getBalance();
if (oldBalance == 0 && newBalance != 0) { // did the height increase?
t.setBalance(t.getBalance() - 1);
}
if (t.getBalance() == -2) { // out of balance – must rotate
if (t.getLeft().getBalance() == -1) {
// single rotation and balance update
// the return value of rotateRight(t) is the new root after the rotation
t = rotateRight(t);
// The new root and its right child always has a balance of 0 after a rotate right.
t.setBalance(0);
t.getRight().setBalance(0);
} else { // double rotation and balance update
// once you get it right here, basically the
// same code can be used in other places including delete
// Check if it is a x insert or a y insert. Update balances accordingly.
if (t.getLeft().getRight().getBalance() == -1) {
t.setLeft(rotateLeft(t.getLeft()));
t = rotateRight(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(1);
} else if (t.getLeft().getRight().getBalance() == 1) {
t.setLeft(rotateLeft(t.getLeft()));
t = rotateRight(t);
t.setBalance(0);
t.getLeft().setBalance(-1);
t.getRight().setBalance(0);
} else {
// t.getLeft().getRight().getBalance() == 0
t.setLeft(rotateLeft(t.getLeft()));
t = rotateRight(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(0);
}
}
}
}
// Cannot be just else because this allows duplicates in the tree.
else if (str.compareToIgnoreCase(t.getItem()) > 0) { // str is bigger than this node.
if (t.getRight() == null) {
oldBalance = 3; // flag value
t.setBalance(t.getBalance() + 1);
} else {
oldBalance = t.getRight().getBalance();
}
t.setRight(insert(str, t.getRight()));
newBalance = t.getRight().getBalance();
if (oldBalance == 0 && newBalance != 0) {
t.setBalance(t.getBalance() + 1);
}
if (t.getBalance() == 2) {
if (t.getRight().getBalance() == 1) {
// the return value of rotateLeft(t) is the new root after the rotation
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
} else {
// Check if it is a x insert or a y insert. Update balances accordingly.
if (t.getRight().getLeft().getBalance() == -1) {
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(1);
} else if (t.getRight().getLeft().getBalance() == 1) {
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(-1);
t.getRight().setBalance(0);
} else { // t.getRight().getLeft().getBalance() == 0
t.setRight(rotateRight(t.getRight()));
t = rotateLeft(t);
t.setBalance(0);
t.getLeft().setBalance(0);
t.getRight().setBalance(0);
}
}
}
}
return t;
}