【数据结构】平衡二叉树

public class BST> {

    
    private class Node{
        public E e;
        public Node left ,right;
        public Node(E e){
            this.e = e;
            left = null;
            right = null;
        }
    }

    private Node root;
    private int size;

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

    public void add(E e){
//        if (root == null){
//            root = new Node(e);
//            size++;
//        }else {
        root = add(root,e);
//        }
    }

    
    private Node add(Node node ,E e ){
//      不包括重复情况
//        if (e.equals(node.e)){
//            return;
//        }else if (e.compareTo(node.e) < 0 && node.left == null){
//            node.left = new Node(e);
//            size++;
//            return;
//        }else if (e.compareTo(node.e) > 0 && node.right ==null){
//            node.right = new Node(e);
//            size++;
//            return;
//        }
//        if (e.compareTo(node.e) < 0){
//            add(node.left,e);
//        }else {
//            add(node.right,e);
//        }
        
        if (node == null){
            size++;
            return new Node(e);
        }if (e.compareTo(node.e) < 0){
            node.left = add(node.left,e);
        }else if (e.compareTo(node.e) > 0){
            node.right = add(node.right,e);
        }
        return node;
    }

    public boolean contains(E e){
        return contains(root,e);
    }

//    看以node为跟的二分搜搜树是否包含元素e
    private boolean contains(Node node ,E e){
        if (node == null){
            return false;
        }
        if (e.compareTo(node.e) == 0){
            return true;
        }else if (e.compareTo(node.e) < 0){
            contains(node.left,e);
        }else {
            contains(node.right,e);
        }
        return false;
    }

    public void preOrder(){
        preOrder(root);
    }

    private void preOrder(Node node){
        if (node == null){
            return;
        }
        System.out.println(node.e);
        preOrder(node.left);
        preOrder(node.right);
    }

    
    public void preOrderNR(){
        Stack stack = new Stack();
        stack.push(root);
        while (!stack.isEmpty()) {
            Node cur = stack.pop();
            System.out.println(cur.e);
            if (cur.left != null)
                stack.push(cur.left);
            if (cur.right != null)
                stack.push(cur.right);
        }
    }

    
    public void postOrder(){
        postOrder(root);
    }

    private void postOrder(Node node){
        if (node == null){
            return;
        }
        postOrder(node.left);
        postOrder(node.right);
        System.out.println(node.e);
    }

    
    public void inOrder(){
        inOrder(root);
    }

    private void inOrder(Node node){
        if (node == null){
            return;
        }
        inOrder(node.left);
        System.out.println(node.e);
        inOrder(node.right);
    }

    public E minMum(){
        if (size == 0){
            throw new IllegalArgumentException("二分搜索树为空");
        }
        return minMum(root).e;
    }

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

    
    public E removeMin(){
        E ret = minMum();
        root = removeMin(root);
        return ret;
    }

    private Node removeMin(Node node){
        if (node.left == null){
//          这里右子树可能为空
            Node rightNode = node.right;
            node.right = null;
            size --;
            return rightNode;
        }
        node.left = removeMin(node.left);
        return node;
    }

    public E removeMax(){
        E ret = maxMum();
        root = removeMin(root);
        return ret;
    }

    private Node removeMax(Node node){
        if (node.right == null){
            Node rightNode = node.left;
            node.right = null;
            size --;
            return rightNode;
        }
        node.right = removeMin(node.right);
        return node;
    }

    public E maxMum(){
        if (size == 0){
            throw new IllegalArgumentException("二分搜索树为空");
        }
        return maxMum(root).e;
    }

    private Node maxMum(Node node){
        if (node.right == null){
            return node;
        }
        return maxMum(node.right);
    }

    public void remove(E e){
        root = remove(root,e);
    }

    private Node remove(Node node,E e){
        if (node == null){
            return null;
        }
        if (e.compareTo(node.e) < 0){
            node.left = remove(node.left,e);
        }else if (e.compareTo(node.e) > 0){
            node.right = remove(node.right,e);
        }else { //e == node.e
            if (node.left == null) {
                Node rightNode = node.right;
                node.right = null;
                size--;
                return rightNode;
            }
            if (node.right == null){
                Node leftNode = node.left;
                node.left = null;
                size --;
                return leftNode;
            }
        }
//      待删除节点均不为空,找到比待删除节点大的最小节点，即待删除节点右子树的最小节点
        Node successor = minMum(node.right);
        successor.right = removeMin(node.right);
        successor.left = node.left;
        node.left = node.right = null;
        return successor;
    }

    
    public void levelOrder(){
        Queue q = new linkedList<>();
        q.add(root);
        while (!q.isEmpty()){
            Node cur = q.remove();
            System.out.println(cur.e);
            if (cur.left != null){
                q.add(cur.left);
            }
            if (cur.right != null){
                q.add(cur.right);
            }
        }

    }

    public int size(){
        return size;
    }

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



    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        generateBSTString(root,0,res);
        return res.toString();
    }

    private void generateBSTString(Node root, int i, StringBuilder res) {
        if (root == null){
            res.append(generateDepthString(i)+"nulln");
            return;
        }
        res.append(generateDepthString(i)+root.e+"n");
        generateBSTString(root.left,i+1,res);
        generateBSTString(root.right,i+1,res);
    }

    private String generateDepthString(int i) {
        StringBuilder res = new StringBuilder();
        for (int j = 0; j < i; j++) {
            res.append("--");
        }
        return res.toString();
    }


}