Algorithm 4 describes how to create a strip set from a box set B.
Firstly an empty strip set S is created. Then we judge whether B contains
boxes that can be accommodated by the residual space
(lr wr hei). If B contains such boxes, a strip s will be created
from B by referring to a similar record or solving Formula (13). Then
the boxes which are included in s will be removed from B. After that,
s will be inserted into S. We repeat creating strips until B contains
no boxes that can be accommodated by the residual space.