f={i=0;it.each{it.reverse i=!i}.flatten()}
println f([[4, 3, 2, 1], [5, 6, 7, 8], [12, 11, 10, 9], [13, 14, 15, 16]])
Zj17aT0wO2l0LmVhY2h7aXQucmV2ZXJzZSBpPSFpfS5mbGF0dGVuKCl9CgpwcmludGxuIGYoW1s0LCAzLCAyLCAxXSwgWzUsIDYsIDcsIDhdLCBbMTIsIDExLCAxMCwgOV0sIFsxMywgMTQsIDE1LCAxNl1dKQo=
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]