平衡二叉树（AVL）

public class AVLTreeDemo {

    public static void main(String[] args) {
        int[] arr = {4, 3, 6, 5, 7, 8};
        int[] arr2 = {10, 12, 8, 9, 7, 6};
        int[] arr3 = {10, 11, 7, 6, 8, 9};
        AVLTree avlTree = new AVLTree();
        for (int i = 0; i < arr3.length; i++) {
            avlTree.add(new Node(arr3[i]));
        }
        avlTree.infixOrder();
        System.out.println(avlTree.getRoot().height());
        System.out.println(avlTree.getRoot().leftHeight());
        System.out.println(avlTree.getRoot().rightHeight());
    }
}

class AVLTree {
    private Node root;

    public Node getRoot() {
        return root;
    }

    public void setRoot(Node root) {
        this.root = root;
    }

    public void add(Node node) {
        if (root == null) {
            root = node;
        } else {
            root.add(node);
        }
    }

    public void infixOrder() {
        if (root != null) {
            root.infixOrder();
        }
    }

    public Node search(int value) {
        if (root == null) {
            return null;
        } else {
            return root.search(value);
        }
    }

    public Node searchParent(int value) {
        if (root == null) {
            return null;
        } else {
            return root.searchParent(value);
        }
    }

    public int delRightTreeMin(Node node) {
        Node target = node;
        while (target.right != null) {
            target = target.right;
        }
        delete(target.value);
        return target.value;
    }

    public void delete(int value) {
        if (root == null) {
            return;
        } else {
            Node targetNode = search(value);
            if (targetNode == null) {
                return;
            }
            if (root.left == null && root.right == null) {
                root = null;
                return;
            }

            Node parent = searchParent(value);
            if (targetNode.left == null && targetNode.right == null) {
                if (parent.left != null && parent.left == targetNode) {
                    parent.left = null;
                } else if (parent.right != null && parent.right == targetNode) {
                    parent.right = null;
                }
            } else if (targetNode.left != null && targetNode.right != null) {
                int minVal = delRightTreeMin(targetNode.left);
                targetNode.value = minVal;
            } else {
                if (targetNode.left != null) {
                    if (parent != null) {
                        if (parent.left.value == value) {
                            parent.left = targetNode.left;
                        } else {
                            parent.right = targetNode.left;
                        }
                    } else {
                        root = targetNode.left;
                    }
                } else {
                    if (parent != null) {
                        if (parent.left.value == value) {
                            parent.left = targetNode.right;
                        } else {
                            parent.right = targetNode.right;
                        }
                    } else {
                        root = targetNode.right;
                    }
                }
            }
        }
    }
}

class Node {
    int value;
    Node left;
    Node right;

    public Node(int value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Node[" +
                "value=" + value +
                ‘]‘;
    }

    public void add(Node node) {
        if (node == null) {
            return;
        }
        if (node.value < this.value) {
            if (this.left == null) {
                this.left = node;
            } else {
                this.left.add(node);
            }
        } else {
            if (this.right == null) {
                this.right = node;
            } else {
                this.right.add(node);
            }
        }
        if (rightHeight() - leftHeight() > 1) {
            if (right != null && right.rightHeight() < right.leftHeight()) {
                right.rightRotate();
                leftRotate();
            } else {
                leftRotate();
            }
            return;//!!!!!
        }
        if (leftHeight() - rightHeight() > 1) {
            if (left != null && left.rightHeight() > left.leftHeight()) {
                left.leftRotate();
                rightRotate();
            } else {
                rightRotate();
            }
        }
    }

    public void infixOrder() {
        if (this.left != null) {
            this.left.infixOrder();
        }
        System.out.println(this);
        if (this.right != null) {
            this.right.infixOrder();
        }
    }

    public Node search(int value) {
        if (value == this.value) {
            return this;
        } else if (value < this.value) {
            if (this.left == null) {
                return null;
            }
            return this.left.search(value);
        } else {
            if (this.right == null) {
                return null;
            }
            return this.right.search(value);
        }
    }

    /**
     * @param value 要找的值
     * @return 要删除节点的父节点 没有返回null
     */
    public Node searchParent(int value) {
        if ((this.left != null && this.left.value == value) ||
                (this.right != null && this.right.value == value)) {
            return this;
        } else {
            if (value < this.value && this.left != null) {
                return this.left.searchParent(value);
            } else if (value >= this.value && this.left != null) {
                return this.right.searchParent(value);
            } else {
                return null;
            }
        }
    }

    public int height() {
        return Math.max(left == null ? 0 : left.height(), right == null ? 0 : right.height()) + 1;
    }

    public int leftHeight() {
        if (left == null) {
            return 0;
        }
        return left.height();
    }

    public int rightHeight() {
        if (right == null) {
            return 0;
        }
        return right.height();
    }

    //左旋转
    private void leftRotate() {
        Node newNode = new Node(value);
        newNode.left = left;
        newNode.right = right.left;
        value = right.value;
        right = right.right;
        left = newNode;
    }

    //右旋转
    private void rightRotate() {
        Node newNode = new Node(value);
        newNode.right = right;
        newNode.left = left.right;
        value = left.value;
        left = left.left;
        right = newNode;
    }
}