Step 1 and Step 2: Sort and group all items as Step 1 and Step 2
of Algorithm 1.
Step 3. Let Z
z be an empty set for zone z, z = 1, 2, . . .,
n. Assign G1 and Gn+1 into the zone with the
picker who has the highest traveling speed,
G2 and Gn+2 into the zone with the picker
who has the second highest traveling speed
and so on, such that every zone has two
groups.