two_sum created by barbchoy - https://repl.it/Br7V/3198

two_sum.rb

# 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

  while i<nums.length
  j=0
  sum_of_two_nums=0
    while j<nums.length
      sum_of_two_nums=nums[i]+nums[j]
      if sum_of_two_nums==0
        pos=[i,j]
        return pos
      end
      j+=1
    end
  i+=1
  end
  return nil
end

# These are tests to check that your code is working. After writing
# your solution, they should all print true.

puts("\nTests for #two_sum")
puts("===============================================")
    puts(
      'two_sum([1, 3, 5, -3]) == [1, 3]: ' + (two_sum([1, 3, 5, -3]) == [1, 3]).to_s
    )
    puts(
      'two_sum([1, 3, 5]) == nil: ' + (two_sum([1, 3, 5]) == nil).to_s
    )
    puts(
      'two_sum([1, 3, 5, -5]) == [2,3]: ' + (two_sum([1, 3, 5, -5]) == [2,3]).to_s
    )
puts("===============================================")