问题描述：已知某工程分解为11个子工程（P1，P2，…,P11），每个子工程的工期，各自工程以及各子工程与总工程之间的关系如下图所示。现在想缩短该工程的总工期，问要缩短那些子工程的工期，才能达到缩短该工程总工期的目标？-Problem descr iption : decomposition of a project known as 11 sub-projects (P1, P2, ..., P11), each for the project, each of the sub-projects and projects with a total of the relationship between, as shown in Fig. Now the project wants to shorten the overall project, who asked to shorten the time limit for the project can be achieved to reduce the total time limit of the target?