AVLTree

你以为爱就是被爱

/**
 * @Classname AVL
 * @Description
 * @Date 2020/1/19 15:02
 * @Author SonnSei
 */
public class AVLTree<K extends Comparable<K>, V> {

    private Node root;
    private int size;

    public AVLTree() {
        root = null;
        size = 0;
    }

    public int getSize() {
        return size;
    }

    public boolean isEmpty() {
        return size == 0;
    }  

    public boolean isBalanced() {
        return isBalanced(root);
    }

    private boolean isBalanced(Node node) {
        if (node == null) return true;
        int balanceFactor = getBalanceFactor(node);
        if (Math.abs(balanceFactor) > 1) return false;
        return isBalanced(node.left) && isBalanced(node.right);
    }

    private int getBalanceFactor(Node node) {
        if (node == null) return 0;
        return getHeight(node.left) - getHeight(node.right);
    }

    private int getHeight(Node node) {
        if (node == null) return 0;
        return node.height;
    }

    // 对节点y进行向右旋转操作，返回旋转后新的根节点x
    //        node                           x
    //       / \                           /   \
    //      x   T4     向右旋转 (y)        z     node
    //     / \       - - - - - - - ->    / \   / \
    //    z   T3                       T1  T2 T3 T4
    //   / \
    // T1   T2
    private Node rightRotate(Node node) {
        Node x = node.left;
        node.left = x.right;
        x.right = node;

        node.height = Math.max(getHeight(node.left), getHeight(node.right)) + 1;
        x.height = Math.max(getHeight(x.left), getHeight(x.right)) + 1;

        return x;
    }

    // 对节点y进行向左旋转操作，返回旋转后新的根节点x
    //    node                          x
    //  /  \                          /   \
    // T1   x      向左旋转 (y)       node   z
    //     / \   - - - - - - - ->   / \   / \
    //   T2  z                     T1 T2 T3 T4
    //      / \
    //     T3 T4
    private Node leftRotate(Node node) {
        Node x = node.right;
        node.right = x.left;
        x.left = node;

        node.height = Math.max(getHeight(node.left), getHeight(node.right)) + 1;
        x.height = Math.max(getHeight(x.left), getHeight(x.right)) + 1;

        return x;
    }

    public void add(K key, V value) {
        root = add(root, key, value);
    }

    private Node add(Node node, K key, V value) {
        if (node == null) {
            size++;
            return new Node(key, value);
        }

        if (key.compareTo(node.key) < 0)
            node.left = add(node.left, key, value);
        else if (key.compareTo(node.key) > 0)
            node.right = add(node.right, key, value);
        else
            node.value = value;

        // 更新height
        node.height = 1 + Math.max(getHeight(node.left), getHeight(node.right));

        int balanceFactor = getBalanceFactor(node);

        //LL
        if (balanceFactor > 1 && getBalanceFactor(node.left) > 0)
            return rightRotate(node);
        //RR
        if (balanceFactor < -1 && getBalanceFactor(node.right) < 0)
            return leftRotate(node);

        //LR
        if (balanceFactor > 1 && getBalanceFactor(node.left) < 0) {
            node.left = leftRotate(node.left);
            return rightRotate(node);
        }
        //RL
        if (balanceFactor < -1 && getBalanceFactor(node.right) > 0) {
            node.right = rightRotate(node.right);
            return leftRotate(node);
        }

        return node;
    }

    public boolean contains(K key) {
        return getNode(root, key) != null;
    }

    private Node getNode(Node node, K key) {
        if (node == null) return null;
        if (key.equals(node.key)) return node;
        if (key.compareTo(node.key) < 0) return getNode(node.left, key);
        return getNode(node.right, key);
    }

    public void set(K key, V newValue) {
        Node node = getNode(root, key);
        if (node != null) node.value = newValue;
    }

    public V get(K key) {
        Node node = getNode(root, key);
        return node == null ? null : node.value;
    }


    public V remove(K key) {

        Node node = getNode(root, key);
        if (node != null) {
            root = remove(root, key);
            return node.value;
        }
        return null;
    }

    private Node remove(Node node, K key) {

        if (node == null)
            return null;

        Node retNode;
        if (key.compareTo(node.key) < 0) {
            node.left = remove(node.left, key);
            retNode = node;
        } else if (key.compareTo(node.key) > 0) {
            node.right = remove(node.right, key);
            retNode = node;
        } else {
            if (node.left == null) {
                Node rightNode = node.right;
                node.right = null;
                size--;
                retNode = rightNode;
            } else if (node.right == null) {
                Node leftNode = node.left;
                node.left = null;
                size--;
                retNode = leftNode;
            }

            // 待删除节点左右子树均不为空的情况
            else {
                Node successor = minimum(node.right);
                successor.right = remove(node.right, successor.key);
                successor.left = node.left;

                node.left = node.right = null;
                retNode = successor;
            }
        }

        if (retNode == null)
            return null;

        retNode.height = 1 + Math.max(getHeight(retNode.left), getHeight(retNode.right));

        int balanceFactor = getBalanceFactor(retNode);

        // 平衡维护
        // LL
        if (balanceFactor > 1 && getBalanceFactor(retNode.left) >= 0)
            return rightRotate(retNode);

        // RR
        if (balanceFactor < -1 && getBalanceFactor(retNode.right) <= 0)
            return leftRotate(retNode);

        // LR
        if (balanceFactor > 1 && getBalanceFactor(retNode.left) < 0) {
            retNode.left = leftRotate(retNode.left);
            return rightRotate(retNode);
        }

        // RL
        if (balanceFactor < -1 && getBalanceFactor(retNode.right) > 0) {
            retNode.right = rightRotate(retNode.right);
            return leftRotate(retNode);
        }

        return retNode;
    }

    private Node minimum(Node node) {
        if (node.left == null)
            return node;
        return minimum(node.left);
    }


    private class Node {
        K key;
        V value;
        Node left, right;
        int height;

        public Node(K key, V value) {
            this.key = key;
            this.value = value;
            left = null;
            right = null;
            height = 1;
        }
    }
}

来源：CSDN

作者：SonnSei

链接：https://blog.csdn.net/weixin_40602200/article/details/104041637