Exercise 4.1
Implement a function incBy:
def incBy(l: List[Int], n: Int): List[Int] = ??? that takes a list of integers and an integer as arguments and increases every element of the list by the given integer. Use the map method.
def incBy(l: List[Int], n: Int): List[Int] = l.map(_ + n) Exercise 4.2
Implement a function gt:
def gt(l: List[Int], n: Int): List[Int] = ??? that takes a list of integers and an integer as arguments and filters elements less than or equal to the given integer out from the list. Use the filter method.
def gt(l: List[Int], n: Int): List[Int] = l.filter(_ > n)Exercise 4.3
Implement a function append:
def append(l: List[Int], n: Int): List[Int] = ??? that takes a list of integers and an integer as arguments and returns a list obtained by appending the integer at the end of the list. Use the foldRight method.
def append(l: List[Int], n: Int): List[Int] =
l.foldRight(List(n))((current, accumulator) => current::accumulator)foldRight's List(n) that first parameter mean starting point for the accumulator. foldRight get second parameter by (current, accumulator) order, foldLeft get second parameter by (accumulator, current). I think the reason is that we're ordering the parameters of the function to be used as parameters according to the actual order of operations.
Exercise 4.4
Implement a function reverse:
def reverse(l: List[Int]): List[Int] = ??? that takes a list of integers and returns a list obtained by reversing the order between the elements. Use the foldLeft method.
def reverse(l: List[Int]): List[Int] =
l.foldLeft(Nil:List[Int])((acc, cur) => cur :: acc)