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Thread: Delete root node in Binary Search Tree

  1. #1
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    Default Delete root node in Binary Search Tree

    Hi everyone,

    I'm learning data structure and this is the example code from the textbook.

    package lab7.part2;
     
    public class BinarySearchTree_Pham {
        TreeNode root;
     
        public BinarySearchTree_Pham() {
            root = null;
        }
     
        public boolean insert(Student_Pham newStudent) {
            TreeNodeWrapper p = new TreeNodeWrapper();
            TreeNodeWrapper c = new TreeNodeWrapper();
            TreeNode n = new TreeNode();
            if(n == null)
                return false;
            else {
                n.node = newStudent.deepCopy();
                n.lc = null;
                n.rc = null;
                if(root == null) {
                    root = n;
                }
                else {
                    findNode(newStudent.getId(), p, c);
                    if(newStudent.getId().compareTo(p.get().node.getId()) < 0)
                        p.get().lc = n;
                    else
                        p.get().rc = n;
                }
                return true;
            }
        } //end insert
     
        public Student_Pham fetch(String id) {
            boolean found;
            TreeNodeWrapper p = new TreeNodeWrapper();
            TreeNodeWrapper c = new TreeNodeWrapper();
            found = findNode(id, p, c);
            if (found == true)
                return c.get().node.deepCopy();
            else
                return null;
        } //end fetch
     
        public boolean delete(String id) {
            boolean found;
            TreeNodeWrapper p = new TreeNodeWrapper();
            TreeNodeWrapper c = new TreeNodeWrapper();
            TreeNode largest;
            TreeNode nextLargest;
            found = findNode(id, p, c);
            if(found == false)
                return false;
            else {
                if(c.get().lc == null && c.get().rc == null) {
                    if (p.get().lc == c.get())
                        p.get().lc = null;
                    else
                        p.get().rc = null;
                } //end case 1
                else if (c.get().lc == null || c.get().rc == null) {
                    if (p.get().lc == c.get()) {
                        if (c.get().lc != null)
                            p.get().lc = c.get().lc;
                        else
                            p.get().lc = c.get().rc;
                    }
                    else {
                        if (c.get().lc != null)
                            p.get().rc = c.get().lc;
                        else
                            p.get().rc = c.get().rc;
                    }
                } // end case 2
                else {
                    nextLargest = c.get().lc;
                    largest = nextLargest.rc;
                    if (largest != null) {
                        while (largest.rc != null) {
                            nextLargest = largest;
                            largest = largest.rc;
                        }
                        c.get().node = largest.node;
                        nextLargest.rc = largest.lc;
                    }
                    else {
                        nextLargest.rc = c.get().rc;
                        if (p.get().lc == c.get())
                            p.get().lc =nextLargest;
                        else
                            p.get().rc = nextLargest;
                    }
                } // end case 3
                return true;
            }
        } // end of delete
     
        public boolean update(String id, Student_Pham newStudent) {
            if(delete(id) == false)
                return false;
            else if (insert(newStudent) == false)
                return false;
            return true;
        } // end update
     
        public void showAll() {
            if (root == null)
                System.out.println("Structure is empty.");
            else
                LNRoutputTraversal(root);
        } //end showAll
     
        private void LNRoutputTraversal(TreeNode root) {
            if (root.lc != null)
                LNRoutputTraversal(root.lc);
            System.out.println(root.node);
            if (root.rc != null)
                LNRoutputTraversal(root.rc);
        }
     
        public class TreeNode {
            private Student_Pham node;
            private TreeNode lc;
            private TreeNode rc;
            public TreeNode() {}
        }
     
        private boolean findNode(String targetKey, TreeNodeWrapper parent, TreeNodeWrapper child) {
            parent.set(root);
            child.set(root);
            if (root == null)
                return true;
            while (child.get() != null) {
                if(child.get().node.getId().compareTo(targetKey) == 0)
                    return true;
                else {
                    parent.set(child.get());
                    if(targetKey.compareTo(child.get().node.getId()) < 0)
                        child.set(child.get().lc);
                    else
                        child.set(child.get().rc);
                }
            } //end while
            return false;
        }
     
        public class TreeNodeWrapper {
            TreeNode treeRef = null;
            public TreeNodeWrapper() {}
            public TreeNode get() {return treeRef;}
            public void set(TreeNode t) {treeRef = t;}
        }
    }

    It cannot handle deleting root node in the tree and my task is to modify it to make it delete root node. Can anyone help me?

    Thank you

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Delete root node in Binary Search Tree

    Do you have the algorithm or list of steps the program must take to solve the problem?
    Once you have that you can try to write the java code to implement it.

    If you have any problems writing the code, post the steps for the algorithm in English and ask the questions you have about writing the code.
    If you don't understand my answer, don't ignore it, ask a question.

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