leetcode.js

// Built from https://github.com/zhiyelee/node-leetcode

/**
 * Converts an array into a Linked List
 * @param  {Array<Number>} arr the array to convert
 * @return {Object}        the linked list object
 */
var createList = arr => {
  var head = { val: null, next: null };
  var current = head;
  arr.forEach(el => {
    current.next = { val: el, next: null };
    current = current.next;
  });

  return head.next;
}

/**
 * Converts an array into a Binary Tree
 * @param  {Array<Number>} arr the array to convert
 * @return {Object}        the binary tree object
 */
var createTree = arr => {
  // 1. check for an empty tree
  if(!arr.length || arr[0] === null) return null;
  var len = arr.length;

  // 2. setup the root node
  var root = { val: arr[0], left: null, right: null };
  // 3. track remaining nodes
  var nodes = arr.slice(1);
  // 4. track remaining children for continuing tree traversal
  var children = [root];
  // 5. track current tree step
  var current = root;

  // 6. loop through remaining children (starting at root node)
  while(children.length) {
    // 7. grab the first child
    current = children.shift();

    // 8. verify we received a valid node
    if(!current || current.val === null) {
      continue;
    }

    // 9. check for left node
    if(nodes.length) {
      current.left = { val: nodes.shift(), left: null, right: null };
      children.push(current.left);
    }

    // 10. check for right node
    if(nodes.length) {
      current.right = { val: nodes.shift(), left: null, right: null };
      children.push(current.right);
    }
  }

  // 11. return the new node tree
  return root;
}