This is an old revision of the document!


4.1. Common list operations

4.1.1.* Write a function which returns true if a list of integers has at least k elements. Use patterns. <code scala> def atLeastk(k: Int, l: List[Int]): Boolean = if (k == 0) ??? else ??? } </code> 4.1.2. Write a function which returns the first n elements from a given list. The function should not be implemented as tail-recursive. <code scala> def take(n: Int, l: List[Int]): List[Int] = ??? take(3,List(1,2,3,4,5)) = 3 </code> 4.1.3. Write a function which drops the first n elements from a given list. The function should not be implemented as tail-recursive. <code scala> def drop(n: Int, l: List[Int]): List[Int] = ??? drop(3,List(1,2,3,4,5)) = List(4,5) </code> 4.1.4. Write a function which takes a predicate p: Int ⇒ Boolean, a list l and returns a sublist of l containing those elements for which p is true. The function should be curried. <code scala> def takeP(p: Int ⇒ Boolean)(l: List[Int]): List[Int] = ??? takeP(_%2 == 0)(List(1,2,3,4,5,6)) = List(2,4,6) </code> 4.1.5. Write a function which uses a predicate to partition (split) a list. <code scala> def part(p: Int ⇒ Boolean)(l: List[Int]): (List[Int], List[Int]) = ??? part(_%2 == 0)(List(1,2,3,4,5,6)) = (List(2,4,6),List(1,3,5)) </code>