Java实现Avl树

Avl树即左右子树的深度【高度】相差不可超过1，所以在插入key的时候，就会出现需要旋转【更改根节点】的操作

下面是源代码：

/*
the define of avltree's node
 */
class MyNode {
    int key, height;
    MyNode left, right;

    MyNode(int d) {
        key = d;
        height = 1;
    }
}

public class MyAvlTree {
    MyNode root;

    /*
    the function of get_tree_height
     */
    int getHeight(MyNode node) {
        if (node == null)
            return 0;
        return node.height;
    }

    /*
    the function of get the max of two numbers
     */
    int max(int a, int b) {
        return (a > b) ? a : b;
    }

    /*
    the function of right rotate subtree rooted y
     */
    MyNode rightRoate(MyNode y) {
        MyNode x = y.left;
        MyNode t = x.right;

        /*
        perform rotation
         */
        x.right = y;
        y.left = t;

        /*
        update the heights
         */
        y.height = max(getHeight(y.left), getHeight(y.right)) + 1;
        x.height = max(getHeight(x.left), getHeight(x.right)) + 1;
        // return new root
        return x;
    }

    /*
    the function of left rotate subtree rooted x
     */
    MyNode leftRoate(MyNode x) {
        MyNode y = x.right;
        MyNode t = y.left;

        /*
        perform rotation
         */
        y.left = x;
        x.right = t;

       /*
       update the heights
        */
        x.height = max(getHeight(x.left), getHeight(x.right));
        y.height = max(getHeight(y.left), getHeight(y.right));
        //return new root
        return x;
    }

    /*
    get balance factor of node n
     */
    int getBalance(MyNode node) {
        if (node == null)
            return 0;
        return getHeight(node.left) - getHeight(node.right);
    }

    /*
    the function of insert
     */
    MyNode insertKey(MyNode n, int key) {
        if (n == null)
            return (new MyNode(key));
        if (key > n.key)
            n.right = insertKey(n.right, key);
        else if (key < n.key)
            n.left = insertKey(n.left, key);
        else
            return n;

        /*
        update height
         */
        n.height = 1 + max(getHeight(n.left), getHeight(n.right));

        //get balance
        int balance = getBalance(n);

        /*
        there are four cases
         */
        //left-left case
        if (balance > 1 && key < n.left.key)
            return rightRoate(n);
        //right-right case
        if (balance > 1 && key > n.right.key)
            return leftRoate(n);
        //left-right case
        if (balance > 1 && key > n.left.key) {
            n.left = leftRoate(n.left);
            return rightRoate(n);
        }
        //right-left case
        if (balance > 1 && key < n.right.key) {
            n.right = rightRoate(n.right);
            return leftRoate(n);
        }
        return n;
    }

    /*
    the functionn of preOrder
     */
    void preOrder(MyNode node) {
        if (node != null) {
            System.out.print(node.key + " ");
            preOrder(node.left);
            preOrder(node.right);
        }
    }

    /*
    the test example
     */
    public static void main(String[] args) {
        MyAvlTree tree = new MyAvlTree();

        //the test
        tree.root = tree.insertKey(tree.root, 10);
        tree.root = tree.insertKey(tree.root, 20);
        tree.root = tree.insertKey(tree.root, 30);
        tree.root = tree.insertKey(tree.root, 40);
        tree.root = tree.insertKey(tree.root, 50);
        tree.root = tree.insertKey(tree.root, 25);

        System.out.println("Preorder traversal" +
                " of constructed tree is : ");
        tree.preOrder(tree.root);
    }
}