Write a method that returns the "pivot" index of a list. We define the pivot index as the index where the sum of the numbers on the left is equal to the sum of the numbers on the right. For instance given [1, 4, 6, 3, 2], the method should return 2, since the sum of the numbers to the left of index 2 is equal to the sum of numbers to the right o…

pivot_index.rb

def pivot_index(ary)
  idx = -1
  left_sum = 0
  right_sum = ary[1..-1].inject(:+)

  #can't find pivot if array's length is less than 3
  if ary.length > 2
    #ignore the first and last element because they only have 1 neighbor
    1.upto(ary.length - 2) do |x|
      left_sum += ary[x-1]
      right_sum -= ary[x]

      if left_sum == right_sum
        idx = x
        break
      end
    end
  end

  idx
end

hi

this is not done in a very efficient way.

refactored the method