The x2 "count.times do" followed by the next is my new favorite way to traverse arrays at two different spots.

dual_array_traversal.rb

# Array = [1,2,-2,1,0], return array of arrays of pairs of indicies of the values that add up to zero

def pairs(array) 
  pairs = []
  traverse = array.count
  
  traverse.times do |i|
    traverse.times do |j|
      # We don't want to check cases where the j value is behind the i value or at the same position
      # Because we don't want to re-check past values or check the same value
      # Next helps us do that
      next if j <= i
      
      pairs << [i, j] if array[i] + array[j] == 0 
    end
  end
  
  pairs
end