A workshop has two machines, and , and needs to prepare pieces.
Piece must be processed for minutes on each machine. Its processing order is determined by :
A, it must be processed on machine first, then on machine .B, it must be processed on machine first, then on machine .Each machine can process at most one piece at a time. Once processing a piece on a machine starts, it cannot be interrupted. A piece may wait between its two stages. The machines may work simultaneously on different pieces.
All pieces are available at time . You may choose when to start each stage, subject to these rules.
Find the minimum time by which all pieces can finish processing on both machines.
A or B.A processes pieces 1, 2, and 3 during , , and . B processes them during , , and . Machine B cannot start before time 2 and needs 6 minutes of processing, so finishing earlier than time 8 is impossible.
A processes piece 1 during , piece 2 during , and piece 3 during . B processes piece 2 during , piece 3 during , and piece 1 during . Piece 1 alone needs 12 minutes across its two stages, so this schedule is optimal.
A processes pieces 1, 2, and 3 during , , and . B processes pieces 3, 1, and 2 during , , and . Each machine has 9 minutes of work, so this schedule is optimal.