SimpleTask__Scala__

// Karol Dziachan

//task1

def flatten[A] (xs:List[List[A]]) : List[A] =
  if(xs == Nil) throw new Exception("Empty list")
  else if (xs.length == 1) xs.head
   else xs.head ::: flatten(xs.tail)


flatten(List(List(1,2,3), List(4,5,6), List(7,8,9))) == List(1,2,3,4,5,6,7,8,9)
flatten(List(List(), List(1,2,3))) == List(1,2,3)
flatten(List(List(4,5,6), List())) == List(4,5,6)
flatten(List())


//task2



def count [A] (x: A, xs: List[A]) : Int =
  if(xs == Nil) throw new Exception("empty list")
  else if(xs.tail == Nil)
    if(xs.head == x) 1
      else 0
  else if(xs.head == x) 1+count(x: A, xs.tail)
  else count(x: A, xs.tail)

count ('a', List('a','l','a')) == 2
count ('a', List('a','l','a', 'a', 'a', 'm', 'a')) == 5
count ('a', List('l')) == 0
count ('a', List('a')) == 1
count(1, List(1,2,4,1,3,2,1)) == 3
count ('a', List())



//task3

def replicate [A] (x: A, n: Int): List[A] =
   if(n==1) List(x)
    else if(n==0) throw new Exception("Nothing")
   else List(x)::: replicate(x, n-1)



replicate("la", 3) == List("la", "la", "la")
replicate("la", 1) == List("la")
replicate("", 3) == List("", "", "")
replicate("la", 0)
replicate("", 0)

//task4


def sqrList (xs: List[Int]): List[Int] =
  if(xs == Nil ) throw new Exception("empty list")
  else if(xs.tail != Nil) ((List(xs.head*xs.head) ::: sqrList(xs.tail)))
    else if (xs.head != Nil ) List(xs.head*xs.head)
  else   xs

sqrList(List(1,2, 3, (-4)))
sqrList(List(1,2,3,4,5))
sqrList(List((-1), 2, 3, 4, (-5)))
sqrList(List())

//task5

def palindrome[A] (xs: List[A]): Boolean =
  if(xs==Nil) throw new Exception("Empty list")
else
  xs==xs.reverse

palindrome(List("a", "l", "a"))
palindrome(List("A", "l", "a"))
palindrome(List("k", "a", "j", "a", "k"))
palindrome(List("k", "a", "r", "o", "l"))
palindrome(List())

//task6

def listLength[A](xs: List[A]): Int =
  if(xs == Nil) throw new Exception ("empty list")
  else if (xs.tail != Nil) 1+listLength(xs.tail)
  else 1

listLength(List(1,2,3,4,5))
listLength(List("k", "a", "r", "o", "l"))
listLength(List("mother"))
listLength(List("mother", "father"))
listLength(List())