节点未添加到二叉搜索树 C#

Question

我尝试在我的 BST 中显示节点，但它们没有显示，所以我试图检查它们是否首先被

添加到 BST 中

using System;

namespace Binary_Search_Tree
{
    class Program
    {
        static void Main(string[] args)
        {
            BinarySearchTree bst = new BinarySearchTree(7);
            bst.Add(new int[] { 4, 15, 2, 6, 14, 16, 10 });

            //bst.preOrderTraversal(bst.root);
            Console.Write(bst.root.left.right);
        }
    }
}

但这是我得到的错误：未处理的异常。 System.NullReferenceException: 对象引用未设置为对象的实例。在 Binary_Search_Tree.Program.Main(字符串[] 参数)

节点未添加到二叉搜索树中。

这是二叉搜索树 Class :

using System;
namespace Binary_Search_Tree
{
    public class BinarySearchTree
    {
        public Node root { get; set; }
        Node currentNode;
        public BinarySearchTree(int data)
        {
            root = new Node(data);
            currentNode = root;
        }

        public void Add(int data)
        {
            Node newNode = new Node(data);
            currentNode = root;
            while (currentNode != null)
            {
                if (newNode.data <= currentNode.data)
                {
                    currentNode = currentNode.left;
                }
                else
                {
                    currentNode = currentNode.right;
                }
            }
            currentNode = newNode;

        }

        public void Add(int[] array)
        {
            for (int i = 0; i < array.Length; i++)
            {
                Add(array[i]);
            }
        }

        public void preOrderTraversal(Node node)
        {
            if (node != null)
            {
                Console.Write(node.data + " ");
                preOrderTraversal(node.left);
                preOrderTraversal(node.right);
            }
        }
    }
}

编辑：节点 Class :

namespace Binary_Search_Tree
{
    public class Node
    {
        public int data { get; set; }
        public Node left { get; set; }
        public Node right { get; set; }

        public Node(int data)
        {
            this.data = data;
            left = null;
            right = null;
        }

    }
}

请问各位大神，请问是什么问题？

Answer 1

添加节点错误。我不打算解决所有问题，但代码应该如下所示。下面的代码未经测试，只是为了显示问题所在。

       public void Add(int data)
        {
            Node newNode = new Node(data);
            currentNode = root;
            while (currentNode != null)
            {
                if (newNode.data <= currentNode.data)
                {
                    currentNode.left = newNode;
                }
                else
                {
                    currentNode.right = currentNode;
                }
            }
            currentNode = newNode;

        }

Answer 2

稍微更改了添加功能，现在可以使用了，我仍然不明白问题出在哪里

public void Add(int data)
        {
            Node newNode = new Node(data);
            currentNode = root;
            while (currentNode != null)
            {
                if (newNode.data <= currentNode.data)
                {
                    if (currentNode.left == null)
                    {
                        currentNode.left = newNode;
                        return;
                    }
                    else
                    {
                        currentNode = currentNode.left;
                    }
                }
                else
                {
                    if (currentNode.right == null)
                    {
                        currentNode.right = newNode;
                        return;
                    }
                    else
                    {
                        currentNode = currentNode.right;
                    }
                }
            }

Answer 3

首先，您的添加节点方法存在一些问题。另外，考虑让你的控制台输出它自己的方法。看一下我的 pre-order 遍历示例

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BST
{
   public class BinarySearchTree
    {
        public Node root;
        public class Node //create a node class within our BinarySearchTree class
        {
            public int NodeData;
            public Node Left;
            public Node Right;

            public void WriteNode(int i) //writes our current node value to the console
            {
                NodeData = i;
                Console.Write(NodeData + "," + " ");
            }
        }
        public BinarySearchTree() //BinarySearchTree construct
        {
            root = null; //assigns the root node within the construct of the BinarySearchTree class
        }

        public void Insert(int i)
        {
            Node newNode = new Node
            {
                NodeData = i
            };

                if (root == null) //begin tree traversal starting at root. Since its pre-order traversal, the order is root->left->right
                {
                root = newNode;
                newNode.WriteNode(i);
                }
            else //root has a value, so begin traversing to find the next available node
            {
                Node current = root;
                Node parent;
                
                while(true)
                {
                    parent = current;
                    if (i < current.NodeData) //traverse down the left side of the tree
                    {
                        current = current.Left;
                        if (current == null)
                        {
                            parent.Left = newNode;
                            newNode.WriteNode(i);
                            break;
                        }
                        else //left node has a value, lets traverse right
                        {
                            current = current.Right;
                            if (current == null)
                            {
                                parent.Right = newNode;
                                newNode.WriteNode(i);
                                break;
                            }
                        }
                    }
                    else if (i > current.NodeData) //current node value cannot be assigned to a left child node if its value is > than its parent or root node. Traverse right
                    {
                        current = current.Right;
                        if (current == null)
                        {
                            parent.Right = newNode;
                            newNode.WriteNode(i);
                            break;
                        }
                    }
                }
            }
            
        }

        static void Main(string[] args)
        {
            BinarySearchTree BSTnums = new BinarySearchTree();
            int[] Numbers = { 45, 10, 32, 26, 8, 54, 32, 19, 12, 15, 18, 11, 35, 46 }; //Numbers array to build tree
            int numLength = Numbers.Length;

            for (int x = 0; x < numLength; x++) //iterates the length of the unsorted array, generates Binary Search Tree based on [] Numbers array.
            {
                BSTnums.Insert(Numbers[x]);
            }
            Console.Read();
        }
    }
}

节点未添加到二叉搜索树 C#

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