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Thread: Can someone verify if this code for deleting a BST works?

  1. #1
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    Default Can someone verify if this code for deleting a BST works?

    	/** Clear tree method
    	 * @param a node
    	 */
    	private void clear(Node x) {
    		if(x.left != null) {
    			x = x.left;
    			clear(x);
    		}
    		if(x.right != null) {
    			x = x.right;
    			clear(x);
    		}
    	}

    And relevant code fragment
    			Node iter = root.left;
    			Node iter2 = root.right;
     
    			// delete left side of tree
    			while(iter != null) {
    				clear(iter);
    					System.out.println(""+iter.value);
    				iter = iter.left;
    			}
     
    			// delete right side of tree
    			while(iter2 != null) {
    				clear(iter2);
    				iter = iter.right;
    			}
     
    			// delete root
    			clear(root);
    			root = null;

    Above code is supposed to delete an entire binary search tree. But I don't know if it's doing it right or not.

    Sorry if it's been posted before. If it doesn't work could you point me in the right direction?

    Thanks.


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Can someone verify if this code for deleting a BST works?

    Assuming your nodes don't have parent references (i.e. you can only descend down the tree, not up), you can easily clear the tree by setting the tree's root to null. This will result in a cascading dereferencing of nodes as their parent nodes get garbage collected.

    However, if this is not the case, your code is a little flawed.
        /** Clear tree method
         * @param a node
         */
        private void clear(Node x) {
            if(x.left != null) {
                x = x.left;
                clear(x);
            }
            if(x.right != null) {
                x = x.right;
                clear(x);
            }
        }
    You're re-assigning the value of x. You shouldn't need to do this (and in fact will ruin the clear method if there is a left and right node).

        /** Clear tree method
         * @param a node
         */
        private void clear(Node x) {
            if(x.left != null) {
                clear(x.left);
            }
            if(x.right != null) {
                clear(x.right);
            }
        }

    There's something else that needs to be taken care of: you actually need to de-reference that node. Simply calling clear doesn't remove that node from the BST. Simply assigning the left and right nodes to null (after clearing them) should do the trick.

  3. #3
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    Default Re: Can someone verify if this code for deleting a BST works?

    Can't believe I didn't see that! Yea my tree only moves down. Thanks a million.

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