Question

in Scala programming,

I've done isPalindrome function, but I get stuck with following problem.

let me know how to improve this, please in order to pass the test class following

CHALLENGE 1: This challenge uses the inbuilt List type in Scala k/ object Challenge1 f /ok A palindrome is a list that is the same forwards as backwards. eg, List(1, 2, 2, 1) Make this function return true if a list is a palindrome. Note, you ARE permitted to use the inbuilt reverse method on Lists. k/ def isPalíndrome [T] (list: List [T]) : Boolean = { list matcht case Nil » true case head :: Nil => true case (list.headlist.last) && isPalindrome(list.tail.reverse.tail.reverse) ok Make this function return true if every entry is bigger than its position in the list. So, List(1, 2, 3) would return true but List(1, 2, 2) would return false because the last entry is at position 2 (remember, lists are zero-indexed) but its value (exactly 2) is not bigger than 2 You will find list.zipwithIndex and list.forall useful def entriesBiggerThanIndex(list:List [Int]): Boolean val list-(1 to ) 50 List.zipwithIndex it should "determine if list entries are bigger than their index" in t Challenge1.entriesBiggerThanIndex(List(1, 2, 3)) should be (true) Challenge1.entriesBiggerThanIndex(List()) should be (true) Challenge1.entriesBiggerThanIndex(List(0, 1, 2)) should be (false) Challenge1.entriesBiggerThanIndex(List(0, 0, 3)) should be (false) Challenge1.entriesBiggerThanIndex((1 to 50).toList ++ (1 to 50).reverse.toList) should be (false)

Answer 1

Lets first see what will the function entriesBiggerThanIndex will do in your case:

def entriesBiggerThanIndex(list: List[Int]): Boolean val list(1 to 50) list.zipWithIndex It will return a List of tuple 2 in which first element will be list element and second element will be its index: Example: List(C1,0), (2,1), (3,2), .. ,(50,49))

Correct Implementation:

def entriesBiggerThanIndex(list: List[Int]): Boolean { ExampLe: list List(1,2,3) list.zipWithIndex will give List((1,0), (2,1), (3,2)) Now applying the exists filter on the list by comparing list entry and its index If any tuple inside the zipped list contains entry <= index. It will return true. But our function wants the opposite of it. That is all entries should be bigger than index. So we put ! to the return value. Thats how our short and concise return statement is generated, Here, List.zipWithIndex- List((1,0), (2,1), (3,2)) listTuple = (1,0) for 1st iteration, then (2,1) for 2nd iteration then (3,2) for 3rd iteration ListTuple.1 1 and listTuple.2-0 for 1st iteration listTuple.-1-2 and listTuple-2-1 for 2nd iteration listTuple.-1-3 and listTuple-2-2 for 3rd iteration So final output is true for this example /7 For handling empty list. if(list.isEmpty) true else !list. zipWithIndex. existsClistTuple => listTuple.-1 <-listTuple..2)

Output:

println(Challenge1.entriesBiggerThanIndex(List(1,2,3))) println(Challenge1.entriesBiggerThanIndex(List))) println(Challenge1.entriesBiggerThanIndex(List(0,1,2))) println(Challenge1.entriesBiggerThanIndex(List(0,0,3))) println(Challenge1.entriesBiggerThanIndex SCALAtrue true false false false (1 to 50).tolist++ (1 to 50).reverse.toList