JAVA Recursively complete the sizeAtDepth for a binary tree. This should return all the total of all nodes below depth of k. One helper function must be used.

public class MyIntSET {

private Node root;

private static class Node {

public final int key;

public Node left, right;

public Node(int key) { this.key = key; }

}

// the number of nodes in the tree, at exactly depth k

// include node n if depth(n) == k

public int sizeAtDepth(int k) {

//TO DO//

return 0;

}

}