var assert = require('assert');

​

function stringFromTree(tree) {

  // fill in

  return tree;

}

​

class Node {

  constructor(value) {

    this.val = value;

    this.left = null;

    this.right = null;

  }

}

​

// Regular binary trees

var tree1 = new Node(4);

tree1.left = new Node(1);

tree1.right = new Node(3);

​

var tree2 = new Node(5);

tree2.left = new Node(10);

tree2.left.left = new Node(17);

tree2.left.right = new Node(3);

tree2.right = new Node(8);

​

// Binary search trees