大学的每个专业都要制定教学计划。假设任何专业都有固定的学习年限，每学年含两学期，每学期的时间长度和学分上限值均相等。每个专业开设的课程都是确定的，而且课程在开设时间的安排必须满足先修关系。每门课程有哪些先修课程是确定的，可以有任意多门，也可以没有。每门课恰好占一个学期。试在这样的前提下设计一个教学计划编制程序。

　　要求：

　　（1）输入参数包括：学期总数，一学期的学分上限，每门课的课程号（固定占3位的字母数字串）、学分和直接先修课的课程号。

　　（2）允许用户指定下列两种编排策略之一：一是使学生在各学期中的学习负担尽量均匀；二是使课程尽可能地集中在前几个学期中。

　　（3）若根据给定的条件问题无解，则报告适当的信息；否则将教学计划输出到用户指定的文件中。计划的表格格式自行设计。-Each university should develop professional teaching program. Assuming any professional years of study are fixed, with two semesters per academic year, the length of time each semester and credits on the limits are equal. Professional courses are offered for each set, and the course set up time arrangements must meet the pre-relationship. Each course which is pre-determined course, can have any number of doors, you can not. Accounted for just one semester of each course. Test this premise in the design of a plan of programming.

Requirements:

(1) Input parameters include: total number of semester, a semester credit limit, number of courses for each course (total 3 fixed alphanumeric string), credits and direct Xian Xiuke the course number.

(2) allows the user to specify one of the following two scheduling strategies: first, the students in each semester of study load as even as possible　second is to make the curriculum as much as possible to focus in previous semester.

(3) If u