In a particular school, each course can only have 1 pre-requisite course.

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* These pre-req courses are represented by a map, for example:

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* {"CS120"="","CS220"="CS120","CS230"="CS220","MA100"="MA102","MA102"="MA100"}

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* Note that if a course has no pre-req, it is represented by the empty string ""

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* So in this example, CS120 has no pre-req course.

* CS220 has a pre-req of 120

* CS230 has a pre-req of 220

* MA100 has a pre-req of MA102

* MA102 has a pre-req of MA100

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* Your job is to write a function that determines how many courses must be taken to take a specific course.

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* So your function should return 0 for "CS120"

* your function should return 1 for "CS220"

* your function should return 2 for "CS230"

* your function should return -1 for "MA102" or "MA100". They are in a pre-req loop, so it is impossible to take any of the courses.

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Language is Java