1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8 9 len: 10 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 len: 20 0 1 2 3 4 5 6 7 8 9 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 len: 30 0 1 2 3 4 5 6 7 8 9 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 0 1 2 3 4 5 6 7 8 9 5 6 7 8 9 len: 40