// in node.js environment.
// you can use ES6 import too.
const leettree = require('leettree')

// initial input value.
const array = [1, 2, 3, null, null, 6]

// deserialize the array into binary tree.
const binaryTree = leettree.deserialize(array)
// TreeNode {
//   val: 1,
//   right: TreeNode {
//     val: 3,
//     right: null,
//     left: TreeNode {
//       val: 6,
//       right: null,
//       left: null
//     }
//   },
//   left: TreeNode {
//     val: 2,
//     right: null,
//     left: null
//   }
// }

// serialize the binary tree back into array.
const array2 = leettree.serialize(binaryTree)
// [1, 2, 3, null, null, 6]

const TreeNode = require('leettree').TreeNode

const root = new TreeNode(1)
root.left = new TreeNode(2)
root.right = new TreeNode(3)
root.right.left = new TreeNode(6)