BST - ReturnKClosestNodesToTarget

package Tree.BinarySearchTree;

import Tree.Node;

import java.util.*;

public class ReturnKClosestNodesToTarget {

    static List<Integer> BSTTraverse(Node root, int target, int k) {
        Queue<Integer> q = new ArrayDeque<>();
        BSTTraverseHelper(root, target, k, q);

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

        return res;
    }

    static void BSTTraverseHelper(Node root, int target, int k, Queue<Integer> q) {
        if(root != null) {
            //Left
            BSTTraverseHelper(root.left, target, k, q);

            //ROOT
            int currDiff = Math.abs(root.data - target);
            if(q.size() <k)
                q.offer(root.data);
            else {
                int maxDiff = Math.abs(q.peek() - target);
                if(maxDiff > currDiff) {
                    q.poll();
                    q.offer(root.data);
                }
            }

            //Right
            BSTTraverseHelper(root.right, target, k, q);
        }
    }

    public static void main(String a[]) {
        Node root = new BinarySearchTree().createTree(Arrays.asList( 2, 4, 3, 1, 6, 5, 7));
        System.out.println(BSTTraverse(root, 6, 4));
    }
}