codility_tape_equilibrium.rb

def solution(a)
  head = a[0]
  tail = a[1...a.size].reduce(&:+)
  min = calc_diff(head, tail)
  (1...a.size).each do |idx|
    head += a[idx]
    tail -= a[idx]
    new_diff = calc_diff(head, tail)
    min = new_diff if new_diff < min
  end
  min
end

def calc_diff(head, tail)
  (head - tail).abs
end