二分搜索树的前序遍历的非递归实现，二分搜索树的层序遍历，Spring MVC拦截器-优快云博客

本文链接：https://blog.youkuaiyun.com/sdfsdfsdds2/article/details/127342080

学习目标：

学习Spring MVC拦截器

二分搜索树的前序遍历的非递归实现，二分搜索树的层序遍历

学习内容：

二分搜索树：

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

public class BST<E extends Comparable<E>> {
    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 int size() {
        return size;
    }

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

    //向二分搜索树中添加新的元素e
    public void add(E e) {
        root = add(root, e);
    }

    //向以node为根的二分搜索树中插入元素E，递归算法
    //返回插入节点后二分搜索树的根
    private Node add(Node node, E 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;
    }

    //看二分搜索树中是否包含元素e
    public boolean contains(E e) {
        return contains(root, e);
    }

    //以node为根的二分搜索树中是否包含元素e,递归算法
    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
            return contains(node.right, e);
    }

    //二分搜索树的前序遍历
    public void preOrder() {
        preOrder(root);
    }

    //前序遍历以node为根的二分搜索树，递归算法
    private void preOrder(Node node) {
        if (node == null)
            return;
        System.out.println(node.e);
        preOrder(node.left);
        preOrder(node.right);
    }

    //二分搜索树的非递归前序遍历
    public void preOrderNR() {
        Stack<Node> stack = new Stack<>();
        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);
        }
    }

    //二分搜索树的中序遍历
    public void inOrder() {
        inOrder(root);
    }

    //中序遍历以node为根的二分搜索树，递归算法
    private void inOrder(Node node) {
        if (node == null) {
            return;
        }
        inOrder(node.left);
        System.out.println(node.e);
        inOrder(node.right);
    }

    //二分搜索树的后序遍历
    public void postOrder() {
        postOrder(root);
    }
    //后序遍历以node为根的二分搜索树，递归算法
    private void postOrder(Node node){
        if(node==null){
            return;
        }
        postOrder(node.left);
        postOrder(node.right);
        System.out.println(node.e);
    }
    //二分搜索树的层序遍历
    public void levelOrder(){
        Queue<Node> 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);
        }
    }

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

    //生成以node为根节点，深度为depth的描述二叉树的字符串
    private void generateBSTString(Node node, int depth, StringBuilder res) {
        if (node == null) {
            res.append(generateDepthString(depth) + "null\n");
            return;
        }
        res.append(generateDepthString(depth) + node.e + "\n");
        generateBSTString(node.left, depth + 1, res);
        generateBSTString(node.right, depth + 1, res);
    }

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

}

学习了SpringMVC的使用技巧，并且通过开发一个用户流量拦截器加深了对其的理解。