L08. Maps in Scala
8.1. Gradebooks as maps
We represent a gradebook as a map which holds, for each student (encoded as String), its grade (an Int). We implement a gradebook as a case class, as follows:
case class Gradebook(book: Map[String,Int])
8.1.1. Add a method +
to the class, which adds a new entry to the gradebook.
def + (entry: (String, Int)): Gradebook = ???
8.1.2. Add a method setGrade
which modifies the grade of a given student. Note that your method should return an updated gradebook, not modify the current one, since the latter is immutable.
def setGrade(name: String, newGrade: Int): Gradebook = ???
8.1.3. Implement a method ++
which merges two gradebooks. You may assume the student entries are unique among the two gradebooks.
def ++(other: Gradebook): Gradebook = ???
8.1.4. Lift the previous assumption by also considering the situation where a student may be part of the two gradebooks. Take the higher of the two grades.
def ++(other: Gradebook): Gradebook = { // the best strategy is to first implement the update of an entry into an existing Map... def updateBook(book: Map[String,Int], pair: (String,Int)): Map[String,Int] = ??? // and then use a fold to perform updates for all pairs of the current map. ??? }
8.1.5. Write a function which returns a map, containing as key, each possible grade (from 0 to 10) and a value, the number of students having that grade. (Hint: follow the same strategy as for the previous exercise).
def gradeNo: Map[Int,Int] = ???
8.2. Polynomials
Consider a polynomial encoded as a map, where each present key denotes a power of X, and a value denotes its coefficient.
Map(2 -> 2, 0 -> 3) // encodes 2*X^2 + 3
Add to your worksheet, the definition below:
case class Polynomial (nonZeroTerms: Map[Int,Int])
8.2.1. Add a method *
which multiplies the polynomial by a given coeficient:
def *(n: Int): Polynomial = ???
8.2.2. Override the toString
method to nicely display a polynomial:
override def toString: String = ???
8.2.3. Implement a method hasRoot
which checks if a given integer is a root of the polynomial.
def hasRoot(r: Int): Boolean = ???
8.2.4. Implement a method +
which adds a given polynomial to this one. Hint - this operation is very similar to gradebook merging.
def +(p2: Polynomial): Polynomial = ???