Binary Tree: ReturnKClosestNodesToTarget

package Tree.BinaryTree;

import Tree.Node;

import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;

class MaxHeapNode {
    Node node;
    int diffFromTarget;

    public MaxHeapNode(Node node, int d) {
        this.node = node;
        diffFromTarget = d;
    }
}

public class ReturnKClosestNodesToTarget {

    static List<Integer> returnKClosestNodesToTarget(Node root, int target, int k) {
        PriorityQueue<MaxHeapNode> maxHeap = new PriorityQueue<>((a,b) -> b.diffFromTarget - a.diffFromTarget);
        traverse(root, target, k, maxHeap);

        List<Integer> res = new ArrayList<>();
        while(!maxHeap.isEmpty()) {
            res.add(maxHeap.poll().node.data);
        }

        return res;
    }

    static void traverse(Node root, int target, int k, PriorityQueue<MaxHeapNode> maxHeap) {
        if( root != null ) {
            //System.out.println("root " + root.data);
            int currDiff = Math.abs(target - root.data);
            if(maxHeap.size() < k) {
                MaxHeapNode n = new MaxHeapNode(root, currDiff);
                maxHeap.offer(n);
            } else {
                MaxHeapNode n = maxHeap.peek();
                int maxDiff = n.diffFromTarget;

                if(maxDiff > currDiff) {
                    n = maxHeap.poll();
                    n.node = root;
                    n.diffFromTarget = currDiff;
                    maxHeap.offer(n);
                }
            }

            traverse(root.left, target, k, maxHeap);
            traverse(root.right, target, k, maxHeap);
        }
    }

    public static void main(String args[]) {
        Node root = new Node(1);
        Node n_2 = new Node(2);
        Node n_3 = new Node(3);
        Node n_4 = new Node(4);
        Node n_5 = new Node(5);
        Node n_6 = new Node(6);
        Node n_7 = new Node(7);
        Node n_8 = new Node(8);
        Node n_9 = new Node(9);
        Node n_10 = new Node(10);


        root.left = n_2;
        root.right = n_3;

        n_2.left = n_4;
        n_2.right = n_5;

        n_3.left = n_6;
        n_3.right = n_7;

        n_4.left = n_8;
        n_4.right = n_9;

        n_5.right = n_10;

        System.out.println(returnKClosestNodesToTarget(root, 2, 7));

    }

}