var assert = require('assert');

​

function TreeNode(val) {

    this.val = val

    this.left = null

    this.right = null

}

​

function columnNodesBinaryTree(root) {

    // add your code here

    return;

}

​

try {

    let root = new TreeNode(3);

    root.left = new TreeNode(9);

    root.right = new TreeNode(20);

    root.right.left = new TreeNode(15);

    root.right.right = new TreeNode(7);

    assert.deepEqual(columnNodesBinaryTree(root), [

        [9],

        [3, 15],

        [20],

        [7]

    ]);

​

    console.log('PASSED: ' + "columnNodesBinaryTree([3, 9, 20, null, null, 15, 7]) should return `[[9], [3, 15], [20], [7]]`");