An approximation algorithm a2 - 1 with absolute performance ratio 3 / 4 is proposed and the asymptotic performance ratio of a2 - 1 applied to the problem in which machines require prepare times is 2 / 3 . another problem is two parallel machines scheduling to maximize the number of just in time jobs . for this problem we give a polynomial time optional algorithm in the case early penalty is larger or equal to late penalty , and it is proofed to be np - had when early penalty is less than late penalty 第二章所讨论的另一个问题是带提前和延误惩罚的两台机排序极大化justintime完工工件数问题,当提前惩罚大于或等于延误惩罚时,本文提出了该问题的一个多项式时间最优算法a _ ( 2 - 2 ) ,从而证明了该问题是一个p问题,当提前惩罚小于延误惩罚时,我们证明了该问题是一个np难的问题。