Simple Problems

add_1_to_n.rb

def add_1_to_n(n)
  return n <= 0 ? 0 : n + add_1_to_n( n - 1 )
end

puts add_1_to_n(10) #=> 55

cards.rb

# create a function that generates a deck of cards
#  a deck has many suits
#  a suit has many cards
#  a card has a suit and a rank

suits = %w{ C D H S }
ranks = [ *2..10, *%w{ J Q K A } ] #splat
card_deck = suits.product(ranks).shuffle
card_deck.first(13)

duplication.rb

ary = ["A", "B", "C", "B", "A"]

#ary.group_by { |e| e }.select { |k, v| v.size > 1 }.map(&:first)
#
#ary.sort.chunk { |e| e }.select { |e, count| count.size > 1 }.map(&:first)

ary.select { |e| ary.count(e) > 1 }.uniq

fizzbuzz.rb

100.times do |n|
  str = ''
  str += 'Fizz' if n % 3 === 0
  str += 'Buzz' if n % 5 === 0
  puts str.length > 1 && str || n
end

palindrome.rb

def palindrome?(value)
  if value.kind_of? String
    value.eql?(value.to_s.reverse)
  elsif value.kind_of? Integer
    value.eql?(value.to_s.reverse.to_i)
  else
    puts "not a string or integer"
    return false
  end
end

#irb(main):028:0> palindrome?('racecar')
#=> true
#irb(main):029:0> palindrome?('liam')
#=> false
#irb(main):030:0> palindrome?(121)
#=> true
#irb(main):031:0> palindrome?(122)
#=> false
#irb(main):032:0> palindrome?(1221)
#=> true
#irb(main):033:0> palindrome?([1233])
#not a string or integer
#=> false

set_and_subset.rb

require 'set'
set = Set.new([1,2,3])

result = Set.new(set) #1,2,3
result << Set.new() # {}

class Set
  def pop
    temp = self.to_a.pop
    self.delete(temp)
    temp
  end
end

set.each do |e, index|
 while set.size >= 1 do
   last_element = set.pop() #=>3
   result << last_element #=> {3}, {2}, {1}
   set.each do |e|
    result << Set.new([e,last_element])
   end
 end
end

tuples.rb

# convert array of tuples to hash
# [['a',1], ['b',2], ['c','3' ]]
# with values as ints
# {"a"=>1, "b"=>2, "c"=>3}

a = [['a',1], ['b',2], ['c','3' ]]
h = Hash[*a.flatten]
 #=> {"a"=>1, "b"=>2, "c"=>"3"} 
h.each do |k,v|
  h[k] = v.to_i 
end
 #=> {"a"=>1, "b"=>2, "c"=>3}