二叉搜索树递归插入不显示任何内容

Question

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;

    }

}

Answer 1

BSTNodes的左、右元素为空。您需要在插入之前创建它们。否则，他们创建一个空的挂起的BSTNode（）并插入它，而不连接到树的其余部分。

您可以更改线路,

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

至

 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 );
    }