Control Flow Exercises

Fill in each of the method bodies. Instructions for each method are in the comments. Do not modify any code at the bottom of the file (it's used for testing).

All the problems from medium on are as difficult as real App Academy admission problems, so don't be discouraged!

Test your code by running it line-by-line in the shell.

Click run to test your code against the specs: successes and errors will appear in the shell. Do your best to correct any failing code before reviewing the solutions.

When you're done, check out the solutions and video walkthrough. Happy solving!

# EASY

# Return the middle character of a string. Return the middle two characters if the word is of even length,
# e.g., middle_substring("middle") => "dd",
# middle_substring("mid") => "i"
def middle_substring(str)
  # your code goes here
end

# Return the number of vowels in a string.
def num_vowels(str)
  # your code goes here
end


# MEDIUM

# Return the argument with all its lowercase characters removed.
def destructive_uppercase(str)
  # your code goes here
end

# Write a method that returns an array containing
# all the elements of the argument array in reverse order.
def my_reverse(arr)
  # your code goes here
end


# HARD

# Write your own version of the join method.
# Assume this method will always receive a
# separator as the second argument.
def my_join(arr, separator)
  # your code goes here
end

# Return an array of integers from 1 to 30 (inclusive), except for each multiple of 3 replace the integer with "fizz", for each multiple of 5 replace the integer with "buzz", and for each multiple of both 3 and 5, replace the integer with "fizzbuzz".
def fizzbuzz
  # your code goes here
end

# DO NOT MODIFY CODE BELOW

$success_count = 0
$failure_count = 0

def deep_dup(arr)
  arr.inject([]) { |acc, el| el.is_a?(Array) ? acc << deep_dup(el) : acc << el }
end

def note_success(returned, invocation, expectation)
  puts "success: #{invocation} => #{expectation}"
  $success_count += 1
end

def note_failure(returned, invocation, expectation)
  puts "failure: #{invocation}: expected #{expectation}, returned #{returned}"
  $failure_count += 1
end

def format_args(args)
  o_args = deep_dup(args)
  o_args.map! do |arg|
    arg = prettify(arg)
    arg.class == Array ? arg.to_s : arg  
  end
  o_args.join(', ')
end

def prettify(statement)
  case statement
  when Float
    statement.round(5)
  when String
    "\"#{statement}\""
  when NilClass
    "nil"
  else
    statement
  end
end

def equality_test(returned, invocation, expectation)
  if returned == expectation && returned.class == expectation.class
    note_success(returned, invocation, expectation)
  else
    note_failure(returned, invocation, expectation)
  end
end

def identity_test(returned, invocation, expectation, args)
  if returned.__id__ == args[0].__id__
    equality_test(returned, invocation, expectation)
  else
    puts "failure: #{invocation}: You did not mutate the original array!"
    $failure_count += 1
  end
end

def method_missing(method_name, *args)
  method_name = method_name.to_s
  expectation = args[-1]
  args = args[0...-1]
  if method_name.start_with?("test_")
    tested_method = method_name[5..-1]
    print_test(tested_method, args, expectation)
  else
    method_name = method_name.to_sym
    super
  end
end

def print_test(method_name, args, expectation)
  returned = self.send(method_name, *args)
  returned = prettify(returned)
  expectation = prettify(expectation)
  args_statement = format_args(args)
  invocation = "#{method_name}(#{args_statement})"
  method_name.include?("!") ? identity_test(returned, invocation, expectation, args) : equality_test(returned, invocation, expectation)
  rescue Exception => e
    puts "failure: #{invocation} threw #{e}"
    puts e.backtrace.select {|t| !t.include?("method_missing") && !t.include?("print_test")}
    $failure_count += 1
end

fizzbuzzed = [1, 2, "fizz", 4, "buzz", "fizz", 7, 8, "fizz", "buzz", 11, "fizz",
13, 14, "fizzbuzz", 16, 17, "fizz", 19, "buzz", "fizz", 22, 23, "fizz", "buzz",
26, "fizz", 28, 29, "fizzbuzz"]

puts "
middle_substring:
" + "*" * 15 + "
"
test_middle_substring("middle", "dd")
test_middle_substring("mid", "i")

puts "
num_vowels:
" + "*" * 15 + "
"
test_num_vowels("Aruba", 3)
test_num_vowels("bcd", 0)
puts "
destructive_uppercase:
" + "*" * 15 + "
"
test_destructive_uppercase("doGgIE", "GIE")
test_destructive_uppercase("HI", "HI")
puts "
my_reverse:
" + "*" * 15 + "
"
test_my_reverse(["a", "b", "c"], ["c", "b", "a"])
test_my_reverse(["a"], ["a"])
puts "
my_join:
" + "*" * 15 + "
"
test_my_join(["k", "i", "t", "t", "y"], "", "kitty")
test_my_join(["dolla", "dolla"], "$", "dolla$dolla")
puts "
fizzbuzz:
" + "*" * 15 + "
"
test_fizzbuzz(fizzbuzzed)
puts "
"
puts "TOTAL CORRECT: #{$success_count} / #{$success_count + $failure_count}"
puts "TOTAL FAILURES: #{$failure_count}"
$success_count = 0
$failure_count = 0

Try running the code. (Click the run button.)