task1.rb

# Takes an array of integers as an argument
# and returns the sum of its elements.
# For an empty array it should return zero.
def sum(array)
  array.reduce(0) {  |res, elem| res + elem }
end
# Takes an array of integers as an argument
# and returns the sum of its two largest elements.
# For an empty array it should return zero.
# For an array with just one element,
# it should return that element.
def max_2_sum(array)
  array_new = []
    while(!array.empty? && array_new.size < 2)
      max_elem = array.max
      array_new << max_elem
      array.delete(max_elem)
    end 
  sum(array_new)
end

# DIFFICULT
# Takes an array of integers
# and an additional integer, n, as arguments
# and returns true
# if any two elements in the array of integers sum to n.
# An empty array should sum to zero by definition.
def sum_to_n?(array, n)
  if (array.empty?)
    if (n == 0)
      true
    else 
      false
    end
  elsif (array.size == 1)
    (array.first == n)
  else equal_sum(array, n)
  end
end

def equal_sum(array, n)
  array_new = []
  0.upto(array.size - 2) do |i|
    (i + 1).upto(array.size - 1) do |j|
      array_new << array[i] << array[j]
      if (equal?(array_new, n))
        return true
      end
      array_new = []
    end
  end
  return false
end

def equal?(array, value)
  sum(array) == value
end