在add方法中需要正确应用rotateRight方法和rotateLeft方法。但是我不知道如何精确地应用它。给定数组的PostOrder Traversal输出不正确。
import static java.lang.Integer.max;
import java.util.Arrays;
public class AVLTree {
private Node root;
/**
* default constructor initializes an empty tree.
*/
public AVLTree() {
root = null;
}
/**
* overloaded constructor builds an AVL tree using the array values
* @param values
*/
public AVLTree(Comparable[] values) {
System.out.println("The given array: " + Arrays.toString(values));
for (Comparable value : values) {
add(value);
}
}
/**
* adds an object into the AVL tree into a position that maintains the BST
* property. Performs the necessary rotations to re-balance any imbalances.
* @param e
*/
public void add(Comparable e) {
Node newNode = new Node();
newNode.data = e;
newNode.left = null;
newNode.right = null;
if (root == null)
{
root = newNode;
}
else
{
root.addNode(newNode);
}
//Left Left Case
if (diff() > 1 && newNode.left.data.compareTo(e) == -1){
rotateRight(newNode);
}
// Right Right Case
if (diff() < -1 && newNode.right.data.compareTo(e) == 1){
rotateLeft(newNode.right);
}
// Left Right Case
if (diff() > 1 && newNode.left.data.compareTo(e) == 1) {
rotateLeft(newNode.left);
rotateRight(newNode);
}
// Right Left Case
if (diff() < -1 && newNode.right.data.compareTo(e) == -1) {
rotateRight(newNode.right);
rotateLeft(newNode);
}
}
/**
* Procedure rightRotate(N)
* i. Define SR the subtree rooted an N.left.right
* ii. Make N the right child of N.left
* iii. Make the root of SR the left child of N
* @param n is the parent
*/
void rotateRight(Node n) {
Node temp = n.left;
Node temp2 = temp.right;
n.right = n;
n.left = temp2;
}
/**
* Procedure leftRotate(N)
* i. Define SL the subtree rooted an N.right.left
* ii. Make N the left child of N.right
* iii. Make the root of SL the right child of N
* @param n
*/
void rotateLeft(Node n) {
Node temp = n.right;
Node temp2 = temp.left;
n.left = n;
n.right = temp2;
}
/**
* This method calculates the difference at each node.
* @param n
* @return - the difference between left subtree and right tree is returned.
*/
int diff(Node n) {
int left_height;
int right_height;
left_height = height(n.left);
right_height = height(n.right);
int difference = left_height - right_height;
return difference;
}
int diff() {
return diff(root);
}
/**
* This method calculates the height based on node
* @param n
* @return - This returns the height of the tree
*/
int height(Node n) {
if (n == null) {
return -1;
}
int height = 1 + max(height(n.right), height(n.left));
return height;
}
int height() {
return height(root);
}
/**
* This method finds the node based on the given user node,
* @param value
* @return - if is it found will return "was found" (true) else, "was not found" (found)
*/
public boolean find(Comparable value) {
Node current = root;
while (current != null) {
int d = current.data.compareTo(value);
if (d == 0) {
System.out.println(value + " was found.");
return true;
} else if (d > 0) {
current = current.left;
} else {
current = current.right;
}
}
System.out.println(value + " was not found.");
return false;
}
/**
* returns a string representation of the tree. Elements are listed using
* post-order traversal. Algorithm Postorder(tree) 1. Traverse the left 2.
* Traverse the right 3. Visit the root.
* @return
*/
@Override
public String toString() {
String temp;
if (root == null) {
return "Tree is empty";
} else {
temp = "(" + root.data;
}
if (root.left.data != null && root.right.data != null) {
temp = temp + " " + root.left.data.toString() + " " + root.right.data.toString();
}
return temp = temp + ")";
}
/**
* This method prints the AVL tree in Post Order Traversal method.
* @param node
*/
void printPostOrder(Node node) {
if (node != null) {
printPostOrder(node.left);
printPostOrder(node.right);
System.out.print(node.data + " ");
}
}
void printPostOrder() {
printPostOrder(root);
}
class Node {
public Node parent;
public Comparable data;
public Node left;
public Node right;
/**
* Inserts a new node as a descendant of this node.
* @param newNode the node to insert
*/
public void addNode(Node newNode) {
int comp = newNode.data.compareTo(data);
if (comp < 0) {
if (left == null) {
left = newNode;
} else {
newNode.parent = this;
left.addNode(newNode);
}
} else if (comp > 0) {
if (right == null) {
newNode.parent = this;
right = newNode;
} else {
newNode.parent = right;
right.addNode(newNode);
}
}
}
}
public static void main(String[] args) {
Integer[] treeArray = {14, 17, 11, 7, 53, 4, 13, 8};
AVLTree treeA = new AVLTree(treeArray);
System.out.println("\nThe tree - Post Order Traversal: ");
treeA.printPostOrder();
System.out.println("\nheight of the tree: " + treeA.height());
System.out.println();
System.out.println("Finding values 1 and 4 in the tree...");
treeA.find(1);
treeA.find(4);
}
}
正确的输出应该用于AVL树的PostOrder遍历， 4、8、13、11、7、53、17、14