为什么在此方法的二叉树插入方法中，根总是为空 [英] Why is the root always null in this method insert method for binary tree

问题描述

我正在尝试为BST类实现递归插入节点方法

Iam trying to implement a recursive insert node method for BST class

 public void insertNode(Node r, Node n)
{
    if(r == null)
    {
        System.out.println("r=n"+ n.data);
        r = n;
    }
    else
    {
        System.out.println("r=! null finding place in tree for "+ n.data);
        if(n.data <= r.data)
        {
            if(r.left == null)
                r.left = n;
            else
                insertNode(r.left, n);
        }
        else
        {
            if(r.right == null)
                r.right = n;
            else
                insertNode(r.right, n);
        }
    }
}

我试图像这样调用此方法:

Im trying to invoke this method like so:

  int[] arrTree = {34, 2, 56, 12, 44, 39, 56, 1};
    BT t = new BT();
    for (int i = 0; i < arrTree.length; i++)
    {
        //System.out.println("Tree Root = "+ t.getRoot());
        BT.Node n =  t.new Node(arrTree[i]);
        t.insertNode(t.root, n);
    }

但是我总是得到以下输出:

But Im always getting this output:

 r=n34
 r=n2
 r=n56
 r=n12
 r=n44
 r=n39
 r=n56
 r=n1

Node是BT的内部类.

Node is an inner class of BT.

经过数小时的运行和尝试不同的操作后，我无法弄清楚我做错了什么.

I cannot figure it out after hours of running and trying different things what Im doing wrong.

推荐答案

从显示的代码来看，我的钱在这里出错了:

Judging by the code you've shown, my money's on the error being here:

public void insertNode(Node r, Node n)
{
    if(r == null)
    {
        System.out.println("r=n"+ n.data);
        r = n; //you overwrite the value of r but never use it
    }

Node r实际上是对t.root所引用内容的单独引用，因此将r替换为另一个值不会改变t.root所引用方法之外的内容.您可以在方法内部修改引用的数据，但不能修改引用本身.

Node r is actually a separate reference to whatever t.root refers to, so replacing r with another value won't change whatever t.root refers to outside the method. You can modify the referenced data inside a method, but not the reference itself.

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