skip_tracks.rb

# tequila version
def skip_tracks(arr, i)
  start = inc = i % arr.size()
  count = 1
  
  while inc > 0 && count < arr.size() do
    c = start
    
    while (c + inc) % arr.size != start
      before = (c - inc) % arr.size()
      arr[before], arr[c] = arr[c], arr[before]
      count = count + 1
      c = c + 1
    end
    count = count + 1
    start = start - 1
  end
end

# short version (works with both Ruby 1.8 and Ruby 1.9)
def skip_tracks_18(arr, i)
  t = (s = arr.size) - (h = i % s)
  arr[0, t], arr[t..s] = arr[h..s], arr[0, h]
end

# shortest version (only works with Ruby 1.9)
def skip_tracks_19(arr, i)
  arr.rotate! i
end