二进制搜索树递归插入不显示任何内容 [英] Binary Search Tree Recursive insert not displaying anything

问题描述

我正在二进制搜索树上做一个小型的Java工作，但是当我将一个节点的递归插入实现到树中并显示它时，我什么也得不到。我已经有一段时间了，我不确定，但我认为这是一个传递参考问题。

I'm doing a small Java work on Binary Search Tree but when I'm implementing the recursive insert of a node into the tree and display it, I don't get anything. I've been on it for a while now, I don't know for sure but I think it's a pass-by-reference problem.

这是我的代码：

public class BST {

    private BSTNode root; 

    public BST() {
        root = null;
    }

    public BSTNode getRoot() {
        return root;
    }

    public void insertR( BSTNode root, Comparable elem ) {

        if ( root == null ) {
            root = new BSTNode( elem );
        }
        else {
            if ( elem.compareTo( root.element ) < 0 ) {
                insertR( root.left, elem );
            } else {
                insertR( root.right, elem );
            }
        }

    }

    public void printInOrder (BSTNode root) {
        if (root != null) {

            printInOrder(root.left);
            System.out.println(root.element);
            printInOrder(root.right);

        }
    }
}

class BSTNode {

    protected Comparable element;
    protected BSTNode left;
    protected BSTNode right;

    protected BSTNode ( Comparable elem ) {

        element = elem;
        left = null;
        right = null;

    }

}

我执行了insertR的系列，其中root是要插入的节点，elem是一个字符串，但它不会打印任何内容，就像树根本没有填充一样。我确定这是我的递归插入的问题，但我不知道在哪里，我需要使用递归插入方法，返回任何我认为是不可能的。

I executed a series of insertR with the root being the node to insert into and the elem is a string but it doesn't print anything out, as if the tree was not filled in at all. I'm sure it's problem with my recursive insert but I'm not sure where, I need to use a recursive insert method that returns nothing which I think is impossible.

任何帮助都会很棒。

推荐答案

你的左，右BSTNodes的元素为null。您需要在插入之前创建它们。否则，他们会创建一个空的BSTNode（）并插入它，而不连接到树的其余部分。

Your left, right element of the BSTNodes are null. You need to create them before inserting into it. Otherwise they create an empty hanging BSTNode() and insert it, without connecting to the rest of the tree.

您可以更改行，

            if ( elem.compareTo( root.element ) < 0 ) {
                insertR( root.left, elem );
            } else {
                insertR( root.right, elem );
            }

到

 if ( elem.compareTo( root.element ) < 0 ) {
        if ( root.left == null )
             root.left = new BSTNode( elem );
        else
            insertR( root.left, elem );
    } else {
        if ( root.right == null )
             root.right = new BSTNode( elem );
        else
             insertR( root.right, elem );
    }

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