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pp:2024:scala:l03 [2024/03/13 17:11]
tudor.condrea created 		pp:2024:scala:l03 [2024/03/13 19:27] (current)
tudor.condrea Am modificat increment sa ia predicat si am scos percentage pentru a da mai mult timp la merge sort
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 ==== 3.1. Common list operations ==== ==== 3.1. Common list operations ====
  
-**3.1.1.** Write a function which returns true if a list of integers has at least k elements. Use patterns. Write a second function which returns true if the list has at least k elements that satisfy a predicate.+**3.1.1.** Write a function which returns true if a list of integers has at least ''​k'' ​elements. Use **patterns**. Write a second function which returns ​''​true'' ​if the list has at least ''​k'' ​elements that satisfy a predicate.
 <code scala> <code scala>
-def atLeastk(k: Int, l: List[Int]): Boolean =+def atLeastk(k: Int, l: List[Int]): Boolean = {
   if (k == 0) ???   if (k == 0) ???
   else ???   else ???
-  ​}+}
   ​   ​
 def atLeastkPred(pred:​ Int => Boolean)(k: Int, l: List[Int]): Boolean = ??? def atLeastkPred(pred:​ Int => Boolean)(k: Int, l: List[Int]): Boolean = ???
 </​code>​ </​code>​
  
-**3.1.2.** Write a function which returns the first ''​n''​ elements from a given list. The function should not be implemented as tail-recursive.+**3.1.2.** Write a function which returns the first ''​n''​ elements from a given list. The function should ​**not** be implemented as tail-recursive.
  
 <code scala> <code scala>
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 def part(p: Int => Boolean)(l: List[Int]): (List[Int], List[Int]) = ??? 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)) // part(_%2 == 0)(List(1,​2,​3,​4,​5,​6)) = (List(2,​4,​6),​List(1,​3,​5))
 +</​code>​
 +
 +**3.1.6.** Write a function that reverses the elements of a list. Use a ''​fold''​ function (determine if it should be right or left).
 +<code scala>
 +def rev(l: List[Int]): List[Int] = ???
 +// rev(List(1,​2,​3,​4,​5,​6)) = List(6,​5,​4,​3,​2,​1)
 </​code>​ </​code>​
  
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 </​code>​ </​code>​
  
-**3.2.4.** Split the list between first names and email domains. What ingredients (auxiliary functions) are necessary? Use either a fold or a tail-recursive function in your implementation. +**(!) 3.2.4.** Implement a function ​that tokenizes a String ​split by a given delimiter ​using ''​foldRight''​. Try to figure out what the accumulator should do.
- +
-<code scala> +
-def namesEmails(list:​ List[Str]): List[(Str, Str)] = ??? +
-</​code>​ +
- +
-**3.2.5.** Identify the list of the employed domain names (e.g. ''​gmail.com''​). Remove duplicates. Use no recursion. +
-<code scala> +
-def domains(l: List[Str]): List[Str] = ??? +
-</​code>​ +
- +
-**(!) 3.2.6.** In some previous exercise you have, most likely, used already defined ​function ​to split the emails. Try implementing ​a split function ​using ''​foldRight''​. Try to figure out what the accumulator should do.+
 <code scala> <code scala>
-def mySplit(l: Str): List[Str] = ???+def mySplit(l: Str, sep: Char): List[Str] = ???
 </​code>​ </​code>​
  
-**3.2.7.** Generalize the former function for any given character. Use it to implement ​a function that return the domains without the dot (ex. ''​gmail''​).+**3.2.5.** Implement ​a function that return the domains without the dot (ex. ''​gmail''​).
 <code scala> <code scala>
-def domain(list: List[Str]): List[Str] = ???+def domains(list: List[Str]): List[Str] = ???
 </​code>​ </​code>​
  
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 Add this type alias to your code before solving the following exercises. Add this type alias to your code before solving the following exercises.
  
-**3.3.1.** Write a function which adds one point to all students ​which have a passing grade (>= 5), and leaves all other grades unchanged.+**3.3.1.** Write a function which adds one point to all students ​that satisfy ​a given predicate ​(ex: grade >= 5), and leaves all other grades unchanged.
 <code scala> <code scala>
-def increment(g:​ Gradebook): Gradebook =+def increment(g:​ Gradebook, p: (Str, Int) => Boolean): Gradebook =
   g.map(???​) ​   g.map(???​) ​
 </​code>​ </​code>​
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 </​code>​ </​code>​
  
-**3.3.3.** Write a function which takes a gradebook and returns the percentage of failed vs. passed students, as a pair (x,y). +**3.3.3.** Write a function which takes a gradebook and returns the list of names which have passed. Use filter and map from Scala.
-<code scala> +
-def percentage(g:​ Gradebook): (Double,​Double) = ??? +
-</​code>​ +
- +
-**3.3.4.** Write a function which takes a gradebook and returns the list of names which have passed. Use filter and map from Scala.+
 <code scala> <code scala>
 def pass(g: Gradebook): List[Str] = ??? def pass(g: Gradebook): List[Str] = ???
 </​code>​ </​code>​
  
-**3.3.5.** Implement merge-sort (in ascending order) over gradebooks:+**3.3.4.** Implement merge-sort (in ascending order) over gradebooks:
 <code scala> <code scala>
 def mergeSort(l:​ Gradebook): Gradebook = { def mergeSort(l:​ Gradebook): Gradebook = {
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 </​code>​ </​code>​
  
-**3.3.6** Write a function which takes a gradebook and reports all passing students in **descending** order of their grade.+**3.3.5** Write a function which takes a gradebook and reports all passing students in **descending** order of their grade.
 <code scala> <code scala>
 def honorsList(g:​ Gradebook): List[Str] = ??? def honorsList(g:​ Gradebook): List[Str] = ???
 </​code>​ </​code>​