alexspark

""" Given a singly linked list, how do you find if there is a loop?
    assumptions:
    - `head` can be None or the first node in a linked list
"""

def is_loop(head):
  if head is None or head.next is None:
    return false
  else:
    first, second = head, head.next

alexspark

let fib = {
  [Symbol.iterator]() {
    let pre = 0, cur = 1;
    return {
      next() {
        [pre, cur] = [cur, pre + cur];
        return { done: false, value: cur }
      }
    }
  }

alexspark

// Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures?
// brute force: for each character, iterate over each character in word, if character is not self and is found, return false. time: O(n^2) where n is # of characters in word, space: O(1);
// first appraoch: for each character, look up visited hash table to see if it exists, if not add it to visited. if exists, return false. return true at end of loop. time: O(n), space: O(n);
let isUnique = (word) => {
  let visited = {};
  for (var char of word) {
    if (!!visited[char]) {
      return false
    } else {
      visited[char] = true;

alexspark

// Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures?

// brute force: for each character, iterate over each character in word, if character is not self and is found, return false. time: O(n^2) where n is # of characters in word, space: O(1);

// first appraoch: for each character, look up visited hash table to see if it exists, if not add it to visited. if exists, return false. return true at end of loop. time: O(n), space: O(n);
let isUnique = (word) => {
  let visited = {};
  for (var char of word) {
    if (!!visited[char]) {
      return false

alexspark

// constants
const NAME = `Alex Park`
console.log(`const: ${NAME}`)

// block scope: var vs let
// best explanation so far:
// https://www.sitepoint.com/joys-block-scoping-es6/
for (var i=0; i<3; i++) {
  var j = i * i
}

alexspark

// iterators
const fib = {
  [Symbol.iterator]() {
    let pre = 0, cur = 1;
    return {
      next() {
        [ pre, cur ] = [cur, pre + cur];
        return {
          done: false, value: cur
        };

alexspark

// Set data structure
let s = new Set();
s.add(1);
s.add(2);
s.add(3);
console.log(s.size);

console.log(s.has(2), s.has(10));

for (let k of s.values()) {

alexspark

class Node
  attr_accessor :value, :left, :right
  def initialize(value)
    @value = value
  end
end

def is_height_balanced?(node)
  return true if node.nil?

alexspark

class Node
  attr_accessor :value, :left, :right
  def initialize(value)
    @value = value
  end
end

def pre_order_traversal(node)
  puts node.value
  pre_order_traversal node.left if node.left

alexspark

class Node
  attr_accessor :value, :left, :right
  def initialize(value)
    @value = value
  end
end

def post_order_traversal(node)
  post_order_traversal node.left if node.left
  post_order_traversal node.right if node.right