//Code assembles a Binary Tree using depth first traversal, taking in the inorder and postorder of the tree to create it
//Definition of a Tree Node
//function TreeNode(val) {
//    this.val = val;
//    this.right = this.left = null;
//}

const buildTree = function(inorder, postorder) {
  let hashmap = [];
  let post_index = postorder.length - 1;
  let in_left = 0;
  let in_right = postorder.length - 1;
  for(let val in inorder) {
    hashmap.push(inorder[val]);

  return helper(in_left, in_right);

  function helper(in_left, in_right) {
    if(in_left > in_right) return null;

    //Find the value of the node, create the new node
    let root_val = postorder[post_index];
    let root = new TreeNode(root_val);

    let index = hashmap.indexOf(root_val);

    //Recursively use the helper function to add nodes to the tree.
    //Base case above will return null because the length of the array won't exist
    post_index--;
    //right first because of post order
    root.right = helper(index + 1, in_right);
    root.left = helper(in_left, index - 1);
    //Root returns the first root so we can observe the tree
    return root;
 }

}