20192314 2020—2021—1 《数据结构与面向对象程序设计》实验八 树

1.参考教材PP16.1,完成链树LinkedBinaryTree的实现（getRight,contains,toString,preorder,postorder）

用JUnit或自己编写驱动类对自己实现的LinkedBinaryTree进行测试，提交测试代码运行截图，要全屏，包含自己的学号信息

课下把代码推送到代码托管平台

程序代码

LinkedBinaryTree

import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class LinkedBinaryTree<T> implements Iterable<T>, BinaryTreeADT<T> {
protected BinaryTreeNode<T> root;//设置根结点
protected int modCount;
protected LinkedBinaryTree<T> left,right;
public LinkedBinaryTree() {
    root = null;
}

public LinkedBinaryTree(T element) {
    root = new BinaryTreeNode<T>(element);
}

public LinkedBinaryTree(T element, LinkedBinaryTree<T> left,
                        LinkedBinaryTree<T> right) {
    root = new BinaryTreeNode<T>(element);
    root.setLeft(left.root);
    root.setRight(right.root);
    this.left = left;

    this.right=right;
}

//调用binarylinktree
public BinaryTreeNode<T> getRootNode() throws EmptyCollectionException {
    if (isEmpty()) {
        throw new EmptyCollectionException("BinaryTreeNode ");
    }
    return root;
}

public LinkedBinaryTree<T> getLeft() {
    return left;
}

public LinkedBinaryTree<T> getRight() {
    return right;
}


public int getHeight()
{
    return height(root);
}

//树的深度计算
private int height(BinaryTreeNode<T> node)
{
    if(node==null){
        return 0;
    }
    else {
        int leftTreeHeight = height(node.getLeft());
        int rightTreeHeight= height(node.getRight());
        return leftTreeHeight>rightTreeHeight ? (leftTreeHeight+1):(rightTreeHeight+1);
    }
}
//获取树根的元素
@Override
public T getRootElement() throws EmptyCollectionException {
    if (root.getElement().equals(null)) {
        throw new EmptyCollectionException("BinaryTreeNode ");
    }
    return root.getElement();
}

@Override
public boolean isEmpty() {
    return (root == null);
}

@Override
public int size() {

    int size = 0;
    if(root.getLeft()!=null){
        size+=1;
    }
    if(root.getRight()!=null){
        size+=1;
    }

    return size;
}

//删除右侧结点
public String removeRightSubtree() throws EmptyCollectionException {
    if (root == null)
        throw new EmptyCollectionException("tree is empty");
    BinaryTreeNode cur = root;
    while (cur.getLeft() != null){
        cur.setRight(null);
        cur = cur.left;
    }
    return super.toString();
}
//删除全部元素
public void removeAllElements() throws EmptyCollectionException {
    if (root == null)
        throw new EmptyCollectionException("tree is empty");
    root = null;
}
//boolean元素查找
@Override
public boolean contains(T targetElement) {
    if(targetElement == find(targetElement))
        return true;
    else
        return false;
}

@Override
// 获取当前元素
public T find(T targetElement) {

    BinaryTreeNode<T> current = findAgain(targetElement, root);

    if (current == null)
        try {
            throw new ElementNotFoundException("LinkedBinaryTree");
        } catch (ElementNotFoundException e) {
            e.printStackTrace();
        }

    return (current.getElement());
}

private BinaryTreeNode<T> findAgain(T targetElement, BinaryTreeNode<T> next) {
    if (next == null)
        return null;

    if (next.getElement().equals(targetElement))
        return next;
    // 运用递归进行子树的查找
    BinaryTreeNode<T> temp = findAgain(targetElement, next.getLeft());

    if (temp == null)
        temp = findAgain(targetElement, next.getRight());

    return temp;
}




//中序输出
@Override
public Iterator<T> iteratorInOrder() {
    ArrayListUnordered<T> tempList = new ArrayListUnordered<T>();
    inOrder(root, tempList);
    return new TreeIterator(tempList.iterator());
}
//前序的输出
public void toPreString(){
    preOrder(root);
}
private void preOrder(BinaryTreeNode root){
    if(null!= root){
        System.out.print(root.getElement() + "\t");
        preOrder(root.getLeft());
        preOrder(root.getRight());
    }
}

//后序输出
public void toPostString(){
    postOrder(root);
}
private void postOrder(BinaryTreeNode root) {
    if (null != root) {
        postOrder(root.getLeft());
        postOrder(root.getRight());
        System.out.print(root.getElement() + "\t");
    }
}


protected void inOrder(BinaryTreeNode<T> node, ArrayListUnordered<T> tempList) {
    if (node != null) {
        inOrder(node.getLeft(), tempList);
        tempList.addToRear(node.getElement());
        inOrder(node.getRight(), tempList);
    }
}

//运用递归方法的前序查找
@Override
public Iterator<T> iteratorPreOrder() {
    ArrayListUnordered<T> tempList = new ArrayListUnordered<T>();
    preOrder(root, tempList);
    return new TreeIterator(tempList.iterator());
}
private void preOrder(BinaryTreeNode<T> node, ArrayListUnordered<T> tempList) {
    if (node != null) {
        tempList.addToRear(node.getElement());
        inOrder(node.getLeft(), tempList);
        inOrder(node.getRight(), tempList);
    }
}
//运用迭代方法的后序查找
@Override
public Iterator<T> iteratorPostOrder() {
    ArrayListUnordered<T> tempList = new ArrayListUnordered<T>();
    postOrder(root, tempList);
    return new TreeIterator(tempList.iterator());
}
private void postOrder(BinaryTreeNode<T> node, ArrayListUnordered<T> tempList) {
    if (node != null) {
        tempList.addToRear(node.getElement());
        inOrder(node.getLeft(), tempList);
        inOrder(node.getRight(), tempList);
    }
}

//递归方法的层序遍历
@Override
public Iterator<T> iteratorLevelOrder() { //递归方法的层序遍历
    ArrayListUnordered<BinaryTreeNode<T>> nodes = new ArrayListUnordered<BinaryTreeNode<T>>();
    ArrayListUnordered<T> tempList = new ArrayListUnordered<T>();
    BinaryTreeNode<T> current;

    nodes.addToRear(root);

    while (!nodes.isEmpty()) {
        current = nodes.removeFirst();

        if (current != null) {
            tempList.addToRear(current.getElement());
            System.out.println(current.element);
            if (current.getLeft() != null)
                nodes.addToRear(current.getLeft());
            System.out.println(current.left);
            if (current.getRight() != null)
                nodes.addToRear(current.getRight());
            System.out.println(current.right);
        } else
            tempList.addToRear(null);
    }

    return new TreeIterator(tempList.iterator());
}
//层序输出
public void toLevelString1(){
    if(root == null)
        return;
    int height = getHeight();
    for(int i = 1; i <= height; i++){
        levelOrder(root,i);
    }
}
private void levelOrder(BinaryTreeNode root,int level){
    if(root == null || level < 1){
        return;
    }
    if(level == 1){
        System.out.print(root.getElement() + "\n");
        return;
    }
    levelOrder(root.getLeft(),level - 1);
    levelOrder(root.getRight(),level - 1);
}
//输出树的方法！！！
@Override
public Iterator<T> iterator() {
    return iteratorInOrder();
}

public String toString() {
    UnorderedListADT<BinaryTreeNode<T>> nodes = new ArrayListUnordered<BinaryTreeNode<T>>();
    UnorderedListADT<Integer> levelList = new ArrayListUnordered<Integer>();

    BinaryTreeNode<T> current;
    String result = "";
    int Depth = this.getHeight();//高度和深度计算
    int possibleNodes = (int) Math.pow(2, Depth + 1);
    int countNodes = 0;

    nodes.addToRear(root);
    Integer curLevel = 0;
    Integer preLevel = -1;
    levelList.addToRear(curLevel);

    while (countNodes < possibleNodes) {
        countNodes = countNodes + 1;
        current = nodes.removeFirst();
        curLevel = levelList.removeFirst();
        if (curLevel > preLevel) {
            result = result+ "\n\n";
            preLevel = curLevel;
            for (int j = 0; j < ((Math.pow(2, (Depth - curLevel))) - 1); j++)
                result = result + " ";
        } else {
            for (int i = 0; i < (Math.pow(2, (Depth - curLevel + 1)) - 1); i++) {
                result = result + " ";
            }
        }
        if (current != null) {
            result = result + (current.getElement()).toString();
            nodes.addToRear(current.getLeft());
            levelList.addToRear(curLevel + 1);
            nodes.addToRear(current.getRight());
            levelList.addToRear(curLevel + 1);
        } else {
            nodes.addToRear(null);
            levelList.addToRear(curLevel + 1);
            result = result + " ";
        }
    }
    return result;
}
//设置右结点
public void setRight(LinkedBinaryTree<T> right) {
    this.right = right;
}

private class TreeIterator implements Iterator<T> {
    private int expectedModCount;
    private Iterator<T> iter;

    //迭代
    public TreeIterator(Iterator<T> iter) {
        this.iter = iter;
        expectedModCount = modCount;
    }


    public boolean hasNext() throws ConcurrentModificationException {
        if (!(modCount == expectedModCount))
            throw new ConcurrentModificationException();

        return (iter.hasNext());
    }


    public T next() throws NoSuchElementException {
        if (hasNext())
            return (iter.next());
        else
            throw new NoSuchElementException();
    }


    public void remove() {
        throw new UnsupportedOperationException();
    }
}

}

BinaryTreeADT

import java.util.Iterator;

public interface BinaryTreeADT<T> {


public T getRootElement() throws EmptyCollectionException ;

public boolean isEmpty();


public int size();


public boolean contains(T targetElement);


public T find(T targetElement);


public String toString();

public Iterator<T> iterator();


public Iterator<T> iteratorInOrder();


public Iterator<T> iteratorPreOrder();


public Iterator<T> iteratorPostOrder();


public Iterator<T> iteratorLevelOrder();

}

LinkedBinaryTreeTest

   import java.util.Iterator;

   public class LinkedBinaryTreeTest {
    public static void main(String[] args) {
    LinkedBinaryTree num1 = new LinkedBinaryTree("2");
    LinkedBinaryTree num2 = new LinkedBinaryTree("0");
    LinkedBinaryTree num3 = new LinkedBinaryTree("1");
    LinkedBinaryTree num4 = new LinkedBinaryTree("8",num1,num3);
    LinkedBinaryTree num5 = new LinkedBinaryTree("3",num2,num4);
    LinkedBinaryTree num6 = new LinkedBinaryTree("0",num4,num5);

    Iterator it;
    System.out.println("right of 8： ");
    System.out.println(num4.getRight());
    System.out.println("Contains 2? ");
    System.out.println(num1.contains("2"));

    System.out.println("PreOrder：  ");
    num6 .toPreString() ;

    System.out.println();

    System.out.println("PostOrder： ");
    num6 .toPostString() ;


    System.out.println(num6.toString());

}

}

EmptyCollectionException

public class EmptyCollectionException extends RuntimeException

{

public EmptyCollectionException (String collection)
{
    super ("The " + collection + " is empty.");
}

}

UnorderedListADT

public interface UnorderedListADT extends ListADT
{

  public void addToFront(T element);

  public void addToRear(T element);

  public void addAfter(T element, T target);
}

ElementNotFoundException

public class ElementNotFoundException extends RuntimeException
{
public ElementNotFoundException (String collection)
{
super ("The target element is not in this " + collection);
}
}

ListADT

import java.util.Iterator;
public interface ListADT extends Iterable
{
public T removeFirst();
public T removeLast();
public T remove(T element);
public T first();
public T last();
public boolean contains(T target);
public boolean isEmpty();
public int size();
public Iterator iterator();
public String toString();
}

ArrayIterator

import java.util.ArrayList;
//使用iterator遍历集合的同时对集合进行修改就会出现java.util.ConcurrentModificationException异常
import java.util.ConcurrentModificationException;
import java.util.Iterator;

public class ArrayIterator<T> extends ArrayList<T> implements Iterator<T> {

int iteratorModCount;
int current;
public ArrayIterator()
{
    iteratorModCount = modCount;
    current = 0;

}
public boolean hasNext() throws ConcurrentModificationException
{
    return super.iterator().hasNext();
}
public T next() throws ConcurrentModificationException
{
    return super.iterator().next();
}

public void remove() throws UnsupportedOperationException
{
    throw new UnsupportedOperationException();
}

}

ArrayListUnordered

public class ArrayListUnordered<T> extends ArrayList<T> implements UnorderedListADT<T> {
@Override
public void addToFront(T element) {
    if (size() == list.length)
        expandCapacity();
    for (int i=rear;i > 0; i--)
        list[i] = list[i - 1];
    list[0] = element;
    rear++;
    modCount++;
}

@Override
public void addToRear(T element) {
    if (size() == list.length)
        expandCapacity();
    list[rear] = element;
    rear++;
    modCount++;
}

@Override
public void addAfter(T element, T target) {
    if (size() == list.length)
        expandCapacity();

    int scan = 0;

    //find the insertion point
    while (scan < rear && !target.equals(list[scan]))
        scan++;
    if (scan == rear)
        try {
            throw new ElementNotFoundException("UnorderedList");
        } catch (ElementNotFoundException e) {
            e.printStackTrace();
        }

    scan++;

    for (int shilt = rear; shilt > scan; shilt--)
        list[shilt] = list[shilt - 1];

    list[scan] = element;
    rear++;
    modCount++;
}

}

ArrayList

import java.util.Arrays;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;


public abstract class ArrayList<T> implements ListADT<T>, Iterable<T>
{
private final static int DEFAULT_CAPACITY = 100;
private final static int NOT_FOUND = -1;

protected int rear;
protected T[] list;
protected int modCount;


public ArrayList()
{
    this(DEFAULT_CAPACITY);
}


public ArrayList(int initialCapacity)
{
    rear = 0;
    list = (T[])(new Object[initialCapacity]);
    modCount = 0;
}


protected void expandCapacity(){
    list = Arrays.copyOf(list,list.length*2);
}


@Override
public T removeLast() throws EmptyCollectionException {
    T result = list[rear-1];
    list[rear]=null;
    rear --;
    return result;
}


@Override
public T removeFirst() throws EmptyCollectionException {
    T result =list[0];
    rear--;
    for(int i = 0; i< rear; i++){
        list[i] = list[i + 1];
    }
    list[rear] = null;
    return result;
}


@Override
public T remove(T element)
{
    T result;
    int index = find(element);

    if (index == NOT_FOUND)
        try {
            throw new ElementNotFoundException("ArrayList");
        } catch (ElementNotFoundException e) {
            e.printStackTrace();
        }

    result = list[index];
    rear--;


    for (int scan=index; scan < rear; scan++)
        list[scan] = list[scan+1];

    list[rear] = null;
    modCount++;

    return result;
}


@Override
public T first() throws EmptyCollectionException
{
    T result = list[0];
    return result;
}


@Override
public T last() throws EmptyCollectionException
{
    T result = list[rear-1];
    return result;
}

@Override
public int size(){
    return rear;

}


@Override
public boolean contains(T target)
{
    return (find(target) != NOT_FOUND);
}


private int find(T target)
{
    int scan = 0;
    int result = NOT_FOUND;

    if (!isEmpty()) {
        while (result == NOT_FOUND && scan < rear)
            if (target.equals(list[scan]))
                result = scan;
            else
                scan++;
    }

    return result;
}




@Override
public boolean isEmpty(){
    if(size() == 0){
        return true;
    }else
        return false;
}



@Override
public String toString(){
    String string = "";
    for (int i = 0;i < rear;i++){
        string += list[i] + " ";
    }
    return string;
}


@Override
public Iterator<T> iterator(){
    return new ArrayListIterator();
}


private class ArrayListIterator implements Iterator<T>
{
    int iteratorModCount;
    int current;


    public ArrayListIterator()
    {
        iteratorModCount = modCount;
        current = 0;
    }


    @Override
    public boolean hasNext() throws ConcurrentModificationException
    {
        if (iteratorModCount != modCount)
            throw new ConcurrentModificationException();

        return (current < rear);
    }


    @Override
    public T next() throws ConcurrentModificationException
    {
        if (!hasNext())
            throw new NoSuchElementException();

        current++;

        return list[current - 1];
    }


    @Override
    public void remove() throws UnsupportedOperationException
    {
        throw new UnsupportedOperationException();
    }

}

}

BinaryTreeNode

public class BinaryTreeNode<T> {

protected T element;
protected BinaryTreeNode<T> left;
protected BinaryTreeNode<T> right;


public BinaryTreeNode(T obj) {
    this.element = obj;
    this.left = null;
    this.right = null;
}


///合并构建声明
public BinaryTreeNode(T obj, LinkedBinaryTree<T> left,
                      LinkedBinaryTree<T> right)throws EmptyCollectionException {
    element = obj;
    if (left == null)
        this.left = null;
    else
        this.left = left.getRootNode();

    if (right == null)
        this.right = null;
    else
        this.right = right.getRootNode();
}


public int numChildren() {
    int children = 0;

    if (left != null)
        children = 1 + left.numChildren();

    if (right != null)
        children = children + 1 + right.numChildren();

    return children;
}

public T getElement() {
    return element;
}

public BinaryTreeNode<T> getRight() {
    return right;
}

public void setRight(BinaryTreeNode<T> node) {
    right = node;
}

public BinaryTreeNode<T> getLeft() {
    return left;
}

public void setLeft(BinaryTreeNode<T> node) {
    left = node;
}

public boolean judge(){
    if(right == null && left == null)
        //叶结点的左侧和右侧都没有结点
        return true;
    else
        return false;
}

}

运行截图

基于LinkedBinaryTree，实现基于（中序，先序）序列构造唯一一棵二㕚树的功能，比如给出中序HDIBEMJNAFCKGL和###后序ABDHIEJMNCFGKL,构造出附图中的树

用JUnit或自己编写驱动类对自己实现的功能进行测试，提交测试代码运行截图，要全屏，包含自己的学号信息

课下把代码推送到代码托管平台

程序代码

import java.util.Scanner;
import java.util.StringTokenizer;

public class CreateTree {
public LinkedBinaryTree<String> CreatTree(String inorder[],String preorder[]){
    LinkedBinaryTree<String> binaryTree = null;
    if(inorder.length == preorder.length && inorder.length != 0 && preorder.length != 0){
        int n = 0;
        //根据前序遍历第一个root 进行中序遍历
        while (!inorder[n].equals(preorder[0])) {
            n++;
        }
        //根据前序遍历第一个root 进行中序遍历
        //左子树的数组输入
        String[] preLeft = new String[n];
        String[] inLeft = new String[n];
        //右子树的数组输入
        String[] preRight = new String[preorder.length - n - 1];
        String[] inRight = new String[inorder.length - n - 1];
        for (int t = 0; t < inorder.length; t++) {
            if (t < n) {
                preLeft[t] = preorder[t + 1];//左子树生成
                inLeft[t] = inorder[t];//左子树生成
            }
            if (t > n) {
                preRight[t - n - 1] = preorder[t];//右子树生成
                inRight[t - n - 1] = inorder[t];//右子树生成
            }
            if(t == n){//
                continue;
            }
        }
       /* //重新生成树
        LinkedBinaryTree<String> left = CreatTree(inLeft, preLeft);
        LinkedBinaryTree<String> right = CreatTree(inRight, preRight);
        binaryTree = new LinkedBinaryTree<String>(preorder[0], left, right);//树的输出
        //   System.out.println(binaryTree.toString());*/
        LinkedBinaryTree<String> left = CreatTree(inLeft, preLeft);
        LinkedBinaryTree<String> right = CreatTree(inRight, preRight);
        binaryTree = new LinkedBinaryTree<String>(preorder[0], left, right);//树的输出
        //   System.out.println(binaryTree.toString());
    }else


    //若不满足以下条件则无法构成一棵树。无法生成树
    {
        binaryTree = new LinkedBinaryTree<>();
    }
    return binaryTree;
}

public static void main(String[] args)
{
    String a,b;
    int i = 0,j = 0;
    Scanner scanner  = new Scanner(System.in);
    System.out.println("Input the PreOrder：");
    a = scanner.nextLine();
    System.out.println("Input the PostOrder：");
    b = scanner.nextLine();
    //分别用" "分割，取出每个字符
    StringTokenizer str1 = new StringTokenizer(a, " ");
    StringTokenizer  str2= new StringTokenizer(b, " ");
    //数组
    String[] string1 = new String[str1.countTokens()];
    String[] string2 = new String[str2.countTokens()];
    //放入数组
    while (str1.hasMoreTokens())
    {
        string1[i] = str1.nextToken();
        i++;
    }


    while (str2.hasMoreTokens())
    {
        string2[j] = str2.nextToken();e(string2,string1);
    System.out.println("The Tree is：");
        j++;
    }


    //中序输出
    //前序输出
    CreateTree ct = new CreateTree();
    LinkedBinaryTree<String> binaryTree = ct.CreatTre
    System.out.println();
    System.out.println(binaryTree.toString());
}

}

运行截图

自己设计并实现一颗决策树

提交测试代码运行截图，要全屏，包含自己的学号信息

课下把代码推送到代码托管平台

程序代码

import java.util.Scanner;

public class PsychologicalTest

{
private LinkedBinaryTree tree;

public PsychologicalTest()
{
    String e1 = "你玩CSGO吗 ?";
    String e2 = "你玩崩坏三吗 ?";
    String e3 = "你经常打竞技排位吗 ?";
    String e4 = "你有对象吗 ?";
    String e5 = "你氪金了吗 ?";
    String e6 = "你喜欢打仓库图吗 ?";
    String e7 = "你的段位达到了大地球吗 ?";
    String e8 = "同道单身狗";
    String e9 = "咱俩无话可聊";
    String e10 = "穷鬼";
    String e11 = "大户人家";
    String e12 = "祝你早日登上大地球";
    String e13 = "nt";
    String e14 = "废物";
    String e15 ="精神小伙";


    LinkedBinaryTree<String> n2, n3, n4, n5, n6, n7, n8, n9,
            n10, n11, n12, n13,n14,n15;

    n8 = new LinkedBinaryTree<String>(e8);
    n9 = new LinkedBinaryTree<String>(e9);
    n4 = new LinkedBinaryTree<String>(e4, n8, n9);

    n10 = new LinkedBinaryTree<String>(e10);
    n11 = new LinkedBinaryTree<String>(e11);
    n5 = new LinkedBinaryTree<String>(e5, n10, n11);

    n12 = new LinkedBinaryTree<String>(e12);
    n13 = new LinkedBinaryTree<String>(e13);
    n6 = new LinkedBinaryTree<String>(e6, n12, n13);

    n14 = new LinkedBinaryTree<String>(e14);
    n15 = new LinkedBinaryTree<String>(e15);
    n7 = new LinkedBinaryTree<String>(e7,n14,n15);

    n2 = new LinkedBinaryTree<String>(e2, n4, n5);
    n3 = new LinkedBinaryTree<String>(e3, n6, n7);

    tree = new LinkedBinaryTree<String>(e1, n2, n3);
}

public void start()
{
    Scanner scan = new Scanner(System.in);
    LinkedBinaryTree<String> current = tree;

    System.out.println ("让我们聊一聊");
    while (current.size() > 1)
    {
        System.out.println (current.getRootElement());
        if (scan.nextLine().equalsIgnoreCase("N"))
            current = current.getLeft();
        else
            current = current.getRight();
    }

    System.out.println (current.getRootElement());
}

public static void main(String[] args){
    PsychologicalTest test = new PsychologicalTest();
    test.start();

}

}

运行截图

输入中缀表达式，使用树将中缀表达式转换为后缀表达式，并输出后缀表达式和计算结果（如果没有用树，正常评分。###如果用到了树，即使有小的问题，也酌情给满分）

提交测试代码运行截图，要全屏，包含自己的学号信息

程序代码

FixTest

  import java.util.Scanner;

  public class FixTest {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    System.out.println("请输入表达式:");
    String s = scan.nextLine();
    Fix fix = new Fix();
    System.out.println("后缀表达式为:\n"+Fix.getrp(s));
    System.out.println("计算结果为:\n"+fix.calrp(Fix.getrp(s)));
}

}

Fix

import java.util.Stack;

public class Fix {
static Stack<Character> op = new Stack<>();

public static Float getv(char op, Float f1, Float f2) {
    if (op == '+') return f2 + f1;
    else if (op == '-') return f2 - f1;
    else if (op == '*') return f2 * f1;
    else if (op == '/') return f2 / f1;
    else return Float.valueOf(-0);
}

public static float calrp(String rp) {
    Stack<Float> v = new Stack<>();
    char[] arr = rp.toCharArray();
    int len = arr.length;
    for (int i = 0; i < len; i++) {
        Character ch = arr[i];
        if (ch >= '0' && ch <= '9') v.push(Float.valueOf(ch - '0'));
        else v.push(getv(ch, v.pop(), v.pop()));
    }
    return v.pop();
}

public static String getrp(String s) {
    char[] arr = s.toCharArray();
    int len = arr.length;
    String out = "";

    for (int i = 0; i < len; i++) {
        char ch = arr[i];
        if (ch == ' ') continue;
        if (ch >= '0' && ch <= '9') {
            out += ch;
            continue;
        }

        if (ch == '(')
            op.push(ch);

        if (ch == '+' || ch == '-') {
            while (!op.empty() && (op.peek() != '('))
                out += op.pop();
            op.push(ch);
            continue;
        }

        if (ch == '*' || ch == '/') {
            while (!op.empty() && (op.peek() == '*' || op.peek() == '/'))
                out += op.pop();
            op.push(ch);
            continue;
        }

        if (ch == ')') {
            while (!op.empty() && op.peek() != '(')
                out += op.pop();
            op.pop();
            continue;
        }
    }
    while (!op.empty()) out += op.pop();
    return out;
}

}

运行截图

实验心得

问题1：子树无法通过链表方式与根节点相连接。

问题1解决方案：
将节点的定义方式更改，从下往上定义节点，在根节点处定义时直接将左右两个子树的根节点连接在根节点上。

问题2：在写决策树时，一开始没有仔细学习，就看了一下老师的决策树代码和简单的听了听，结果写的时候根本写不出来

问题2解决方案：乱写了几次实验后，我意识到自己就这么写确实写不出来，于是我重新看了看有关决策树的博客，并请教了同学，才实现了决策树。