def insertion_sort(a)
  (0..(a.length - 1)).each do |j|
    key = a[j]
    i = j - 1
    while (i >= 0) && (a[i] > key)
      a[i + 1] = a[i]
      i = i - 1
    end
    a[i + 1] = key
  end
end