I have written a code of Binary Search tree that extends comparable and implements an interface. The code for leaves and the helper method countLeaves (included down here), makes sure that all of the test goes through except for one, heightIsLogOfNumLeavesTreeIsPerfect().
// TODO: Look at the Leaves and the helper method to leaves and see how I should change it so that this test goes through aswell.
//EDIT: I have added the whole tree class
java.lang.AssertionError:
Expected: <2>
but: was <0>
Expected :<2>
Actual :<0>
import org.junit.Test;
import org.junit.Before;
import org.junit.Rule;
import org.junit.rules.Timeout;
import static org.junit.Assert.*;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.CoreMatchers.*;
import java.util.Arrays;
import java.util.stream.IntStream;
/**
* Test class for a tree.
*/
public class TreeTest{
@Rule public Timeout globalTimeout = Timeout.seconds(5);
Tree<Integer> tree;
int[] elementsInTree;
int[] elementsNotInTree;
@Before
public void setUp() {
/**
* This tree should look like this:
*
* 8
* / \
* 3 10
* / \ \
* 1 6 14
* / \ /
* 4 7 13
*/
tree = new Tree<>();
elementsInTree = new int[] {8, 10, 14, 13, 3, 1, 6, 4, 7};
for (int elem : elementsInTree) {
tree.insert(elem);
}
elementsNotInTree = new int[] {34, -3, -10, 12, 74, 5};
}
@Test
public void heightIsLogOfNumLeavesTreeIsPerfect() {
// For a perfect tree, tree.height() == log2(tree.leaves()
// Arrange
Tree<Integer> tree = new Tree<>();
int[] elements = new int[] {8, 3, 10, 1, 6, 9, 14};
int numLeaves = 4;
int logNumLeaves = (int) Math.round(Math.log(numLeaves) / Math.log(2));
for (int elem : elements) {
tree.insert(elem);
}
// Act
int height = tree.height();
// Assert
assertThat(height, equalTo(logNumLeaves));
}
}
**
* An interface describing a generic Comparable
*/
public interface BSTInterface <T>{
boolean search(T elem);
boolean insert(T elem);
int size();
int height();
int leaves();
}
/**
* An Binary Search tree implementation of the comparable interface.
* @param <T>
*/
public class Tree <T extends Comparable <T>> implements BSTInterface <T>{
private int size;
private Node root;
public class Node{
private Node Left;
private Node Right;
private T data;
public Node(T data){
this.data = data;
}
public Node getRight(){
return Right;
}
public Node getLeft() {
return Left;
}
public T getData() {
return data;
}
}
public Tree (){
size = 0;
root = null;
}
/**
* Test for presence of a value.
* @param elem
* @return true/false
*/
@Override
public boolean search(T elem) {
if(root == null ||elem == null){
return false;
}
Node node = root;
while(true){
if(node.data.compareTo(elem) > 0){
if(node.Right == null){
return false;
} else{
node = node.Right;
}
} else if(node.data.compareTo(elem) == 0){
break;
} else{
if(node.Left== null){
return false;
}
else{
node = node.Left;
}
}
}
return true;
}
/**
* Add value to tree; duplicates are not allowed.
* Return true if the element is not already present (and is thus inserted),
* false otherwise.
*
* @param elem
* @return true/false
*/
@Override
public boolean insert(T elem) {
if (elem == null){
return false;
}
if (root == null){
root = new Node(elem);
size++;
return true;
}
Node node = root;
while (true){
if (node.data.compareTo(elem) > 0) {
if (node.Right == null){
node.Right = new Node(elem);
size++;
break;
} else {
node = node.Right;
}
} else if (node.data.compareTo(elem) == 0) {
return false;
} else {
if (node.Left == null){
node.Left = new Node(elem);
size++;
break;
} else {
node = node.Left;
}
}
}
return true;
}
/**
* the number of elements in the tree
* @return size.
*/
@Override
public int size() {
return size;
}
/**
* The height of the tree.
* The empty tree and the tree with only the root node both have height 0.
* @return the height of the tree.
*/
@Override
public int height() {
return countHeight(root);
}
/**
* Helper method for height
*/
private int countHeight(Node node){
if(node == null) {
return 0;
}
return Math.max(countHeight(node.Left), countHeight(node.Right));
}
/**
* The number of leaves in the tree.
* @return the amount of leaves the tree have.
*/
@Override
public int leaves() {
return countLeaves(root);
}
/**
* Helper method for leaves
*/
private int countLeaves(Node node) {
if (node == null) {
return 0;
}
if (node.Left == null && node.Right == null) {
return 1;
}
return countLeaves(node.Left) + countLeaves(node.Right);
}
/**
* A string describing the tree
* @return
*/
public String toString(){
String str = "[" + helpToString(root);
if (str.length() > 1) {
str = str.substring(0, str.length() - 2);
} return str + "]";
}
/**
* Helper method for toString
*/
private String helpToString(Node node) {
String str = "";
if (node != null) {
str += helpToString(node.Right);
str += node.data + ", ";
str += helpToString(node.Left);
}
return str;
}
}
Your countHeight method can return either zero or a maximum of two returns, and there are no other operations in it. You can't get a value greater of zero out of zeros just by using max function.
You should return -1 for an empty tree and max(height(left) + 1, height(right) + 1) otherwise. Each +1 accounts for length of corresponding parent-child edge.
(Mathematically speaking, height of an "empty" tree is usually undefined, but defining it as -1 in this case helps a lot so let's stick to that.)