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# Write a method that will take a string as input, and return a new
# string with the same letters in reverse order.
#
# Don't use String's reverse method; that would be too simple.
#
# Difficulty: easy.

def reverse(string)
  i=0
  reversed_string=""

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# Write a method that takes an integer `n` in; it should return
# n*(n-1)*(n-2)*...*2*1. Assume n >= 0.
#
# As a special case, `factorial(0) == 1`.
#
# Difficulty: easy.

def factorial(n)
  factorialn=1
  i=n

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# Write a method that takes in a string. Return the longest word in
# the string. You may assume that the string contains only letters and
# spaces.
#
# You may use the String `split` method to aid you in your quest.
#
# Difficulty: easy.

def longest_word(sentence)
  words=sentence.split(' ')

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# Write a method that takes in an integer `num` and returns the sum of
# all integers between zero and num, up to and including `num`.
#
# Difficulty: easy.

def sum_nums(num)
  sum=0
  i=0
  while i<num+1
  sum=sum+i

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# Write a method that will take in a number of minutes, and returns a
# string that formats the number into `hours:minutes`.
#
# Difficulty: easy.

def time_conversion(minutes)
  hour=0
  mins=0
  string_hr_mins=""
  hour=minutes/60

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# Write a method that takes a string and returns the number of vowels
# in the string. You may assume that all the letters are lower cased.
# You can treat "y" as a consonant.
#
# Difficulty: easy.

def count_vowels(string)
  i=0

  num_vowels=0

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# Write a method that takes a string and returns true if it is a
# palindrome. A palindrome is a string that is the same whether written
# backward or forward. Assume that there are no spaces; only lowercase
# letters will be given.
#
# Difficulty: easy.

def palindrome?(string)
  i=0
  palindrome_or_no=true

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# Write a method that takes a string in and returns true if the letter
# "z" appears within three letters **after** an "a". You may assume
# that the string contains only lowercase letters.
#
# Difficulty: medium.

def nearby_az(string)
  i=0
  a_pos=0
  while i<string.length

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# Write a method that takes an array of numbers. If a pair of numbers
# in the array sums to zero, return the positions of those two numbers.
# If no pair of numbers sums to zero, return `nil`.
#
# Difficulty: medium.

def two_sum(nums)
  pos=[]
  i=0

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# Write a method that takes in a number and returns true if it is a
# power of 2. Otherwise, return false.
#
# You may want to use the `%` modulo operation. `5 % 2` returns the
# remainder when dividing 5 by 2; therefore, `5 % 2 == 1`. In the case
# of `6 % 2`, since 2 evenly divides 6 with no remainder, `6 % 2 == 0`.
#
# Difficulty: medium.

def is_power_of_two?(num)