DIY: All Nodes Distance K in Binary Tree

Problem statement

We are given a binary tree (with a root node root), a target node, and an integer value, kk.

Return a list of the values of all nodes that are kk distance from the target node.

Input

The following is an example input:

    3
   / \
  5   1
  |  /  \
  2 15   7
 / \
7   4 

target = 5 
kk = 2

Output

The following is an example output:

[7,4,1]

The nodes that are a distance 2 from the target node 5 have the values 7, 4, and 1.

Coding exercise

For this coding exercise, you need to implement the distance_k(root, target, kk) function, where root is the root node of the binary tree and target is where we start calculating the distance kk. The function will return a list of the values of all the nodes that are kk distance from the target node.