实现一个二分搜索树

package structures;

import java.util.LinkedList;
import java.util.Stack;

/**
 * 左子树小于该节点 右子树大于该节点 重复元素不添加
 *
 * @param <E>
 */
public class BST<E extends Comparable<E>> {
    private class Node {
        public E e;
        public Node left;
        public Node right;

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

    private int size;
    private Node root;

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

    public int getSize() {
        return size;
    }

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

    /**
     * //向二分搜索树中添加元素
     * public void add(E e) {
     * if (root == null) {
     * root = new Node(e);
     * size ++;
     * } else {
     * add(root, e);
     * }
     * }
     * <p>
     * <p>
     * * 使用递归的逻辑添加元素
     * * 递归终止的条件
     * * 1 添加的元素已存在
     * * 2 添加的元素小于该节点且其左子树为null
     * * 3 添加的元素大于该节点且其右子树为null
     * private void add(Node root, E e) {
     * if (root.e.equals(e)) {
     * return;
     * } else if (e.compareTo(root.e) < 0 && root.left == null) {
     * root.left = new Node(e);
     * size ++;
     * return;
     * } else if (e.compareTo(root.e) > 0 && root.right == null ) {
     * root.right = new Node(e);
     * size ++;
     * return;
     * }
     * <p>
     * if (e.compareTo(root.e) < 0) {
     * add(root.left, e);
     * }else {
     * add(root.right, e);
     * }
     * }
     */

    //使用递归 考虑到根节点为null的情况
    public void add(E e) {
        root = add(root, e);
    }

    /**
     * 当该节点子树为Null时作为返回条件
     *
     * @param node
     * @param e
     * @return
     */
    private Node add(Node node, E e) {
        if (node == null) {
            node = new Node(e);
            size++;
            return node;
        }

        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;
    }

    //查找是否包含该元素
    public boolean contains(E e) {
        return contains(root, 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) {
            return contains(node.left, e);
        } else /*e.compareTo(node.e) > 0*/ {
            return contains(node.right, e);
        }
    }

    //前序遍历
    public void preOrder() {
        preOrder(root);
    }

    private void preOrder(Node node) {

        /**
         *       5
         *      / \
         *     3   8
         *    / \   \
         *   2   4    10
         */

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

    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);
    }

    //深度优先
    public void preOrderNR() {
        Stack<Node> stack = new Stack<>();
        if (root != null) {
            stack.push(root);
        }

        while (!stack.isEmpty()) {
            Node cur = stack.pop();
            System.out.println(cur.e);
            if (cur.right != null) {
                stack.push(cur.right);
            }

            if (cur.left != null) {
                stack.push(cur.left);
            }
        }
    }

    // 层级优先
    public void leverOrder() {
        LinkedList<Node> queue = new LinkedList<>();
        queue.add(root);

        while (!queue.isEmpty()) {
            Node cur = queue.remove();
            System.out.println(cur.e);
            if (cur.left != null) {
                queue.add(cur.left);
            }
            if (cur.right != null) {
                queue.add(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);
    }

    //获取最小值
    public E minimum() {
        if (size == 0) {
            throw new IllegalArgumentException("BST is empty");
        }
        return minimum(root).e;
    }

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

    public E maximum() {
        if (size == 0) {
            throw new IllegalArgumentException("BST is empty");
        }

        return maximum(root).e;
    }

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

        return maximum(node.right);
    }

    //删除最小元素节点
    public E removeMin() {
        E minimum = minimum();
        root = removeMin(root);
        return minimum;
    }

    //删除最小元素 并返回其右子树
    private Node removeMin(Node node) {
        if (node.left == null) {
            Node rightNode = node.right;
            node.right = null;
            //删除元素维护一下size
            size--;
            return rightNode;
        }

        node.left = removeMin(node.left);
        return node;
    }

    public E removeMax() {
        E maximum = maximum();
        root = removeMax(root);
        return maximum;
    }

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

        node.right = removeMax(node.right);
        return node;
    }

    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);
            return node;
        } else if (e.compareTo(node.e) > 0) {
            node.right = remove(node.right, e);
            return node;
        } 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;
            }

            Node successor = minimum(node.right);
            successor.right = removeMin(node.right);
            successor.left = node.left;
            node.right = node.left = null;

            return successor;
        }
    }

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

    private void generateBSTString(Node node, int dep, StringBuilder builder) {
        if (node == null) {
            builder.append(generateDep(dep) + "null\n");
            return;
        }

        builder.append(generateDep(dep) + node.e + "\n");
        generateBSTString(node.left, dep + 1, builder);
        generateBSTString(node.right, dep + 1, builder);
    }

    private String generateDep(int dep) {

        StringBuffer stringBuffer = new StringBuffer();
        for (int i = 0; i < dep; i++) {
            stringBuffer.append("--");
        }

        return stringBuffer.toString();
    }
}