Array equi in ruby

equi.rb

def equi(arr)
  return 0 if arr.empty?

  left, right = 0, arr.inject{|sum, n| sum + n}

  equi_indices=[]

  arr.each_with_index do |val,i|
    left += val
    equi_indices << i if right == left
    right -= val
  end

  return -1 if equi_indices.empty?
  equi_indices
end

indices = [
  [-7, 1, 5, 2,-4, 3, 0],
  [2, 4, 6],
  [2, 9, 2],
  [1,-1, 1,-1, 1,-1, 1],
  []
]

indices.each do |x|
  puts "%p => %p" % [x, equi(x)]
end