Solution to Codility demo problem, finding equilibrium index of an array

equi.rb

def sums_before(src)
    dest = [0]
    src.each_with_index do |item, index|
        dest[index + 1] = dest[index] + item
    end
    dest
end

def equi ( arr )
    sums_left = sums_before(arr)
#    p sums_left
    arr.reverse!
    sums_right = sums_before(arr); sums_right.reverse!
#    p sums_right
    
    arr.each_with_index do |item, index|
        if sums_left[index] == sums_right[index + 1]
            return index
        end
    end
    return -1    
end