You should now be able to edit the TwoThreeIntSet class. Finish implementing the functions contains and put. Each recursive function already handles the case when the node is a 2-node. You must add code (at the TODO comment) to handle the case when the node is a 3-node . Each TODO has some comments to help guide you. Make sure to read all the comments in the source file for extra instructions. In particular:

You are only allowed to change or add to the code in the recursive helper functions for put and contains. If you feel that you need to change code anywhere else, email your instructor with an explanation of the change you want to make and why you feel it is necessary/helpful. My response will most likely be no, but if I know WHY you want to make the change I might be able to provide some guidance.

You may not modify the function headers of any of the functions already present.

You may not add any fields to the TwoThreeIntSet class.

package hw3;

import java.util.LinkedList;

public class TwoThreeIntSet {

private class Node {

int[] items; // the keys/items in the node

Node[] subtrees; // the children of this node

int nodeType; // the node type (2, 3, or 4)

/**

* Create a new node with item as the key and two subtrees

*

* @param item

* the key/item for the node

* @param left

* the root of the subtree less than the item

* @param right

* the root of the subtree greater than the item

*/

public Node(int item, Node left, Node right) {

items = new int[3];

subtrees = new Node[4];

subtrees[0] = left;

subtrees[1] = right;

nodeType = 2;

items[0] = item;

}

/**

* Creates a new leaf with item as the key.

*

* @param item

* the key/item for the leaf.

*/

public Node(int item) {

this(item, null, null);

}

/**

* Returns true if this node is a leaf

*

* @return true if this node is a leaf.

*/

public boolean isLeaf() {

return subtrees[0] == null;

}

}

private Node root;

public TwoThreeIntSet() {

}

// DO NOT MODIFY ANYTHING ABOVE THIS LINE

public boolean contains(int item) {

return contains(root, item);

}

private boolean contains(Node n, int item) {

// The base case here is empty tree. The item is not in the empty tree.

if (n == null)

return false;

// If the node is a 2-node, use normal BST search.

if (n.nodeType == 2) {

if (item < n.items[0])

return contains(n.subtrees[0], item);

if (item > n.items[0])

return contains(n.subtrees[1], item);

return true;

}

else if (n.nodeType == 3) {

// TODO

// If the node is a 3-node, we must check both items in this node. If neither is

// the item we are looking for, we must decide which of the three subtrees to

// search next.

throw new RuntimeException("Implement me");

}

// If this node is not a 2-node or a 3-node, this is an error

else

throw new RuntimeException("ERROR: " + n.nodeType + "-node found while searching");

}

/**

* Inserts item into the 2-3 tree.

*

* @param item

* the number to be inserted into the tree.

*/

public void put(int item) {

/*

* If the tree is empty, create a new leaf node for the item. It is also the

* root of the tree.

*/

if (root == null)

root = new Node(item);

/*

* Otherwise, we will be inserting the item in a pre-existing leaf using a

* recursive helper function.

*/

else {

root = put(root, item);

/*

* The recursive helper function returns a 2-3 tree where the root might be a

* 4-node. Check for this and split if necessary.

*/

if (root.nodeType == 4) {

Node left = new Node(root.items[0], root.subtrees[0], root.subtrees[1]);

Node right = new Node(root.items[2], root.subtrees[2], root.subtrees[3]);

root = new Node(root.items[1], left, right);

}

}

}

/**

* A recursive helper function.

*

* @param n

* the root of a 2-3 tree into which we will insert a number

* @param item

* the number to be inserted.

* @return the root of new tree with item inserted. Note that this root might

* now be a 4 node.

*/

private Node put(Node n, int item) {

/*

* First check if n contains item. If it does, there is nothing to do and we can

* return the root of this subtree unchanged

*/

int itemCount = n.nodeType - 1;

for (int i = 0; i < itemCount; i++) {

if (n.items[i] == item)

return n;

}

/*

* Because we always insert into a pre-existing leaf, the base case here is a

* tree with one node (the root is a leaf).

*/

if (n.isLeaf()) {

// If the node is a 2-node, insert the new item to its left or right.

if (n.nodeType == 2) {

if (item < n.items[0]) {

n.items[1] = n.items[0];

n.items[0] = item;

} else {

n.items[1] = item;

}

n.nodeType = 3;

}

else if (n.nodeType == 3) {

// TODO

// Turn this into a 4-node and return it since you are allowed

// to temporarily have a 4-node as a the root.

throw new RuntimeException("Implement me");

}

else

throw new RuntimeException("ERROR: " + n.nodeType + "-node found while inserting");

return n;

}

// If not a leaf node, we will need to insert in one of our subtrees.

else {

if (n.nodeType == 2) {

if (item < n.items[0]) {

Node result = put(n.subtrees[0], item);

// if the resulting root is not a 4-node, we can insert it as our new left.

if (result.nodeType != 4) {

n.subtrees[0] = result;

}

// otherwise, we need to fix it by splitting it

else {

Node newLeft = new Node(result.items[0], result.subtrees[0], result.subtrees[1]);

Node newMiddle = new Node(result.items[2], result.subtrees[2], result.subtrees[3]);

n.items[1] = n.items[0];

n.items[0] = result.items[1];

n.subtrees[2] = n.subtrees[1];

n.subtrees[1] = newMiddle;

n.subtrees[0] = newLeft;

n.nodeType = 3;

}

} else {

Node result = put(n.subtrees[1], item);

// if the resulting root is not a 4-node, we can insert it as our new right.

if (result.nodeType != 4) {

n.subtrees[1] = result;

}

// otherwise, we need to fix it by splitting it

else {

Node newMiddle = new Node(result.items[0], result.subtrees[0], result.subtrees[1]);

Node newRight = new Node(result.items[2], result.subtrees[2], result.subtrees[3]);

n.items[1] = result.items[1];

n.subtrees[2] = newRight;

n.subtrees[1] = newMiddle;

n.nodeType = 3;

}

}

return n;

} else if (n.nodeType == 3) {

// TODO

throw new RuntimeException("Implement me!");

} else

throw new RuntimeException("ERROR: " + n.nodeType + "-node found while inserting");

}

}

// DO NOT MODIFY ANYTHING BEOW THIS LINE

/*

* Returns the height of the tree.

*

* @return the height of the tree.

*/

public int getHeight() {

return getHeight(root);

}

private int getHeight(Node n) {

if (n == null)

return -1;

int subtreeHeight = getHeight(n.subtrees[0]);

if (subtreeHeight == -2)

return -2;

for (int i = 1; i < n.nodeType; i++)

if (getHeight(n.subtrees[i]) != subtreeHeight)

return -2;

return subtreeHeight + 1;

}

/*

* Returns the level order of the two three tree as a String. The string is a

* comma separated list of nodes where each node is a | separated list of keys

* inside of parentheses. For example, after inserting 1, 2, 3, 4, and 0 into an

* an empty 2-3 tree, the level order returned would be the String

* "(0|1),(2),(3|4)"

*/

public String levelOrder() {

LinkedList q = new LinkedList();

StringBuilder result = new StringBuilder();

boolean firstNode = true;

if (root != null)

q.addLast(root);

while (!q.isEmpty()) {

if (firstNode)

firstNode = false;

else

result.append(',');

Node current = q.removeFirst();

result.append('(');

result.append(current.items[0]);

int itemCount = current.nodeType - 1;

for (int i = 1; i < itemCount; i++) {

result.append('|');

result.append(current.items[i]);

}

result.append(')');

if (!current.isLeaf()) {

for (int i = 0; i <= itemCount; i++)

q.addLast(current.subtrees[i]);

}

}

return result.toString();

}

// A tiny main that inserts 10-19 into an emtpy TwoThreeIntSet

// And prints out the level order after each insertion.

public static void main(String[] args) {

TwoThreeIntSet t = new TwoThreeIntSet();

for (int i = 10; i < 20; i++) {

t.put(i);

System.out.println(t.levelOrder());

}

}

}