[16,21,11,8,12,22]
[16,21,11] [8,12,22]
[16,21] [11] [8,12] [22]
[16] [21] [11] [8] [12] [22]
[16,21] [11] [8,12] [22]
[11,16,21] [8,12,22]
[8,11,12,16,21,22]
O(nlogn)