Question

Python 3

Write a function named inverse that takes a single parameter, a dictionary. In this dictionary each key is a student, represented by a string. The value of each key is a list of courses, each represented by a string, in which the student is enrolled.

The function inverse should compute and return a dictionary in which each key is a course and the associated value is a list of students enrolled in that course.

For example, the following would be correct input and output.

>>> student_courses = {'Elise':[],'Nelson':['CS100','MATH111'],'Justin':['CS100']}

>>> print(inverse(student_courses)) {'CS100': ['Nelson', 'Justin'], 'MATH111': ['Nelson']}

Answer 1

#code.py
def inverse(d):
    res = dict()
    for key in d.keys():
        for x in d[key]:
            if not res.get(x):
                res[x] = [key]
            else:
                res[x].append(key)
    return res

#Testing
student_courses = {'Elise':[],'Nelson':['CS100','MATH111'],'Justin':['CS100']}
print(inverse(student_courses))

{'CS100': ['Nelson', 'Justin'], 'MATH111': ['Nelson']}