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| - | ===== L09. Maps in Scala ===== | + | ===== 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: | ||
| + | |||
| + | <code scala> | ||
| + | case class Gradebook(book: Map[String,Int]) | ||
| + | </code> | ||
| + | |||
| + | **8.1.1.** Add a method ''+'' to the class, which adds a new entry to the gradebook. | ||
| + | <code scala> | ||
| + | def + (entry: (String, Int)): Gradebook = ??? | ||
| + | </code> | ||
| + | |||
| + | **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. | ||
| + | <code scala> | ||
| + | def setGrade(name: String, newGrade: Int): Gradebook = ??? | ||
| + | </code> | ||
| + | |||
| + | **8.1.3.** Implement a method ''++'' which merges two gradebooks. You may assume the student entries are unique among the two gradebooks. | ||
| + | <code scala> | ||
| + | def ++(other: Gradebook): Gradebook = ??? | ||
| + | </code> | ||
| + | |||
| + | **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. | ||
| + | <code scala> | ||
| + | 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. | ||
| + | ??? | ||
| + | } | ||
| + | </code> | ||
| + | |||
| + | **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). | ||
| + | <code scala> | ||
| + | def gradeNo: Map[Int,Int] = ??? | ||
| + | </code> | ||
| + | |||
| + | |||
| + | ==== 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. | ||
| + | <code scala> | ||
| + | Map(2 -> 2, 0 -> 3) // encodes 2*X^2 + 3 | ||
| + | </code> | ||
| + | |||
| + | Add to your worksheet, the definition below: | ||
| + | <code scala> | ||
| + | case class Polynomial (nonZeroTerms: Map[Int,Int]) | ||
| + | </code> | ||
| + | |||
| + | **8.2.1.** Add a method ''*'' which multiplies the polynomial by a given coeficient: | ||
| + | <code scala> | ||
| + | def *(n: Int): Polynomial = ??? | ||
| + | </code> | ||
| + | |||
| + | **8.2.2.** Override the ''toString'' method to nicely display a polynomial: | ||
| + | <code scala> | ||
| + | override def toString: String = ??? | ||
| + | </code> | ||
| + | |||
| + | **8.2.3.** Implement a method ''hasRoot'' which checks if a given integer is a root of the polynomial. | ||
| + | <code scala> | ||
| + | def hasRoot(r: Int): Boolean = ??? | ||
| + | </code> | ||
| + | |||
| + | **8.2.4.** Implement a method ''+'' which adds a given polynomial to this one. Hint - this operation is very similar to gradebook merging. | ||
| + | <code scala> | ||
| + | def +(p2: Polynomial): Polynomial = ??? | ||
| + | </code> | ||