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I had some trouble getting this challenge to run (and I had to create an internal TreeNode class to avoid errors). TreeNode has a constructor that takes in an Integer and makes it the .value
I used array slicing this time, and I made a function to do the slicing.
Here’s my code:
import java.lang.*;
import java.util.Arrays;
public class BalancedBST {
public static Integer[] slice(Integer[] arr, int start, int afterEnd) {
int length = afterEnd - start;
Integer[] part = new Integer[length];
int j = 0;
for (int i = start; i < afterEnd; i++) {
part[j] = arr[i];
j++;
}
return part;
}
public static TreeNode balancedBst(Integer[] a) {
if ((a == null) || (a.length < 1)) {
return null;
}
else if (a.length == 1) {
return new TreeNode(a[0]);
}
else {
int mid = a.length / 2; // integer division
TreeNode node = new TreeNode(a[mid]);
node.left = balancedBst(slice(a, 0, mid));
node.right = balancedBst(slice(a, mid + 1, a.length));
return node;
}
}
public static void main(String[] args){
Integer[] a = {1,2,3,4,5,6,7,8};
TreeNode balancedTree = balancedBst(a);
balancedTree.print();
}
/*
public static class TreeNode {
public Integer value;
public TreeNode left; // initialized to null
public TreeNode right; // initialized to null
public TreeNode() {
this.value = null;
}
public TreeNode(Integer value) {
this.value = value;
}
public void print() {
System.out.print(this.value);
if (!(this.left == null && this.right == null)) {
System.out.print(" -> ");
if (this.left != null) {
System.out.print(this.left.value);
if (this.right != null) {
System.out.print(",");
}
}
if (this.right != null) {
System.out.print(this.right.value);
}
System.out.println();
if (this.left != null) {
this.left.print();
}
if (this.right != null) {
this.right.print();
}
}
else {
System.out.println();
}
}
}
*/
}
version without slicing
public static TreeNode balancedBst(Integer[] a, int start, int afterEnd) {
if ((a == null) || start >= afterEnd) {
return null;
}
else if ((start + 1) == afterEnd) {
return new TreeNode(a[start]);
}
else {
int mid = (start + afterEnd) / 2; // integer division
TreeNode node = new TreeNode(a[mid]);
node.left = balancedBst(a, start, mid);
node.right = balancedBst(a, mid + 1, afterEnd);
return node;
}
}
public static TreeNode balancedBst(Integer[] a) {
return balancedBst(a, 0, a.length);
}
I had the same issue.
The code would only run if I created a static TreeNode class inside the other class,
but I had to delete that when I submitted the challenge.
internal TreeNode class (taken from JavaScript version)
public static class TreeNode {
public Integer value;
public TreeNode left;
public TreeNode right;
public TreeNode(value) { //constructor
this.value = value;
this.left = null;
this.right = null;
}
print() {
// outputs node values going down
// the left side of the tree first
// then working right
if (this.left != null) {
System.out.println(this.value + " -> " + this.left.value);
this.left.print();
}
if (this.right != null) {
System.out.println(this.value + " -> " + this.right.value);
this.right.print();
}
}
}
) below.
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