avl-promise/src/utils.js

Largely copied from avl (https://www.npmjs.com/package/avl), but with a Promise-based comparator!

/**
 * Prints tree horizontally
 * @param  {Node}                       root
 * @param  {Function(node:Node):String} [printNode]
 * @return {String}
 */
export function print (root, printNode = (n) => n.key) {
  var out = [];
  row(root, '', true, (v) => out.push(v), printNode);
  return out.join('');
}

/**
 * Prints level of the tree
 * @param  {Node}                        root
 * @param  {String}                      prefix
 * @param  {Boolean}                     isTail
 * @param  {Function(in:string):void}    out
 * @param  {Function(node:Node):String}  printNode
 */
function row (root, prefix, isTail, out, printNode) {
  if (root) {
    out(`${ prefix }${ isTail ? '└── ' : '├── ' }${ printNode(root) }\n`);
    const indent = prefix + (isTail ? '    ' : '│   ');
    if (root.left)  row(root.left,  indent, false, out, printNode);
    if (root.right) row(root.right, indent, true,  out, printNode);
  }
}


/**
 * Is the tree balanced (none of the subtrees differ in height by more than 1)
 * @param  {Node}    root
 * @return {Boolean}
 */
export function isBalanced(root) {
  if (root === null) return true; // If node is empty then return true

  // Get the height of left and right sub trees
  var lh = height(root.left);
  var rh = height(root.right);

  if (Math.abs(lh - rh) <= 1 &&
      isBalanced(root.left)  &&
      isBalanced(root.right)) return true;

  // If we reach here then tree is not height-balanced
  return false;
}

/**
 * The function Compute the 'height' of a tree.
 * Height is the number of nodes along the longest path
 * from the root node down to the farthest leaf node.
 *
 * @param  {Node} node
 * @return {Number}
 */
function height(node) {
  return node ? (1 + Math.max(height(node.left), height(node.right))) : 0;
}