added assignment 6 ex 4

README.md

@@ -57,6 +57,13 @@
 [Files](src/Lesson5)
 - Lists
 - High order functions
+- 
+### Lesson 6 - Tuples and comprehensions
+[Files](src/Lesson6)
+- Tuples
+- For-comprehension
+- Yield
+- Flatmap
 
 ### Midterm preparation
 [Files](src/MidTermPrep1)

src/Assignment6/Ex1.sc

@@ -0,0 +1,17 @@
+def flattenList(list: List[Any]): List[Any] = {
+  list.foldRight(List.empty[Any])(
+    (e, acc) => {
+      e match {
+        case l: List[Any] => flattenList(l) concat acc
+        case _ => e::acc
+      }
+    }
+  )
+}
+
+assert(
+  flattenList(
+    List(List(1,1), 2, List(3, List(5, 8)))
+  ) == List(1,1,2,3,5,8)
+)
+

src/Assignment6/Ex2.sc

@@ -0,0 +1,38 @@
+
+def isPrime(i: Int): Boolean =
+    i match {
+        case i if i <= 1 => false
+        case 2 => true
+        case _ => !(2 to (i - 1)).exists(x => i % x == 0)
+    }
+
+def primeSum(max: Int): List[(Int, Int)] =
+    for {
+        i <- (1 to max).toList
+        j <- (1 to max).toList
+        if (isPrime(i + j))
+    } yield (i, j)
+
+
+def uniquePermutations(permutations: List[(Int, Int)]): List[(Int, Int)] = {
+  permutations match {
+    case Nil => Nil
+    case (a, b)::rest if rest contains(b, a) => uniquePermutations(rest)
+    case head::rest => head::uniquePermutations(rest)
+  }
+}
+
+def uniquePermutations2(permutations: List[(Int, Int)]): List[(Int, Int)] = {
+  permutations.foldRight(List.empty[(Int, Int)])(
+    (e, acc) => {
+      e match {
+        case (a, b) if acc contains (b, a) => acc
+        case _ => e::acc
+      }
+    }
+  )
+}
+
+val perms = primeSum(10)
+uniquePermutations(perms)
+uniquePermutations2(perms)

src/Assignment6/Ex3.sc

@@ -0,0 +1,22 @@
+val cities = List("Paris", "London", "Berlin", "Lausanne")
+val relatives = List("Grandma", "Grandpa", "Aunt Lottie", "Dad")
+val travellers = List("Pierre-Andre", "Rachel")
+
+def generatePostcards(cities: List[String], relatives: List[String], travellers: List[String]): List[String] = {
+  for (t <- travellers;
+       r <- relatives;
+       c <- cities) yield s"Dear $r, Wish you were here in $c! Love, $t"
+}
+
+def generatePostcards2(cities: List[String], relatives: List[String], travellers: List[String]): List[String] = {
+  for (t <- travellers;
+       r <- relatives;
+       c <- cities;
+       if r.startsWith("G")) yield s"Dear $r, Wish you were here in $c! Love, $t"
+}
+
+val cards: List[String] = generatePostcards(cities, relatives, travellers)
+println(cards.mkString("\n"))
+
+val cards2: List[String] = generatePostcards2(cities, relatives, travellers)
+println(cards2.mkString("\n"))

src/Assignment6/Ex4.sc

@@ -0,0 +1,39 @@
+def inCheck(q1: (Int, Int), q2: (Int, Int)) =
+    q1._1 == q2._1 || // same row
+    q1._2 == q2._2 || // same column
+    (q1._1 - q2._1).abs == (q1._2 - q2._2).abs // on diagonal
+
+def isSafe(queen: (Int, Int), queens: List[(Int, Int)]) =
+    queens forall (q => !inCheck(queen, q))
+
+def queens(n: Int): List[List[(Int, Int)]] = {
+    def placeQueens(k: Int): List[List[(Int, Int)]] =
+        if (k == 0)
+            List(List())
+        else
+            for {
+                queens <- placeQueens(k - 1)
+                column <- 1 to n
+                queen = (k, column)
+                if isSafe(queen, queens)
+            } yield queen :: queens
+
+    placeQueens(n)
+}
+
+def printChessBoard(solutions: List[List[(Int, Int)]]): String = {
+  val sols: List[String] = for ((sol, i) <- solutions.zipWithIndex) yield {
+    val lines: IndexedSeq[String] = for (y <- 1 to sol.length) yield {
+      val line: IndexedSeq[String] = {
+        for (x <- 1 to sol.length) yield {
+          if (sol contains (y, x)) "♕" else "_"
+        }
+      }
+      line.mkString("|", "|", "|")
+    }
+    s"Solution $i:\n" + lines.mkString("\n")
+  }
+  sols.mkString("\n\n")
+}
+
+println(printChessBoard(queens(4)))

src/Lesson6/Comprehension.sc

@@ -0,0 +1,18 @@
+(2 to 10).foreach(i =>
+  (2 to 10)
+    .filter(j => i % j == 0)
+    .foreach(j =>
+      println(s"$i is an integer multiple of $j")
+    )
+)
+
+val positions = for (
+  col <- 'a' to 'h';
+  row <- 1 to 8
+) yield (col, row)
+
+val whites = for (
+  col <- 'a' to 'h';
+  row <- 1 to 8;
+  if ((col - 'a' + row) % 2 == 0)
+) yield (col, row)

src/Lesson6/Ex_6.1.sc

@@ -0,0 +1,40 @@
+def filter[T](func: T => Boolean, list: List[T]): List[T] = {
+  list match {
+    case Nil => Nil
+    case e::rest if func(e) => e::filter(func, rest)
+    case _::rest => filter(func, rest)
+  }
+}
+
+def partition[T](func: T => Boolean, list: List[T]): (List[T], List[T]) = {
+  list match {
+    case Nil => (List.empty[T], List.empty[T])
+    case e::rest => {
+      val part = partition(func, rest)
+      if (func(e)) {
+        (e::part._1, part._2)
+      } else {
+        (part._1, e::part._2)
+      }
+    }
+  }
+}
+
+def partition[T](func: T => Boolean, list: List[T]): (List[T], List[T]) = {
+  list.foldRight((List.empty[T], List.empty[T]))(
+    (e: T, prev: (List[T], List[T])) => {
+      if (func(e)) {
+        (e::prev._1, prev._2)
+      } else {
+        (prev._1, e::prev._2)
+      }
+    }
+  )
+}
+
+
+val b = (1 to 10).toList
+
+filter((x: Int) => x % 2 == 0, b)
+
+partition((x: Int) => x % 2 == 0, b)

src/Lesson6/Primes.sc

@@ -0,0 +1,29 @@
+def time(f: => Unit => Any): Long = {
+  val start = System.currentTimeMillis()
+  f()
+  val end = System.currentTimeMillis()
+  end - start
+}
+
+def timeVerbose(s: String)(f: => Unit => Any): Unit = {
+  println(s"[$s] Measuring time...")
+  val duration = time(f)
+  println(s"[$s] It took ${duration}ms")
+}
+
+def isPrime(i: Int): Boolean =
+  i match {
+    case i if i <= 1 => false
+    case 2 => true
+    case _ => !(2 until i).exists(x => i%x == 0)
+  }
+
+def primeSum(max: Int)(isPrimeFunc: Int => Boolean): List[(Int, Int)] = {
+  for (i <- (1 to max).toList;
+       j <- (1 to max).toList;
+       if isPrimeFunc(i + j)) yield (i, j)
+}
+
+timeVerbose("Normal Prime"){
+  primeSum(1000)(isPrime)
+}

src/Lesson6/Translations.sc

@@ -0,0 +1,25 @@
+val q: List[Int] = List(1, 2, 3)
+val p: List[Int] = List(4, 5, 6)
+
+// 1.
+for (x <- q) yield x * 2
+q.map(x => x * 2)
+
+// 2.
+for (x <- q if x != 2) yield x * 2
+q.filter(x => x !=2).map(x => x * 2)
+
+// 3.
+for (x <- q;
+     y <- p) yield (x, y)
+q.flatMap(x => p.map(y => (x, y)))
+
+// 4.
+for (x <- q if (x < 2);
+     y <- p) yield (x, y)
+q.filter(x => x < 2).flatMap(x => p.map(y => (x, y)))
+
+
+for (x <- 1 to 2;
+     y <- 'a' to 'b') yield (x, y)
+(1 to 2).flatMap(x => ('a' to 'b').map(y => (x, y)))

src/Lesson6/Tuples.sc

@@ -0,0 +1,13 @@
+def merge(x: List[Int], y: List[Int]): List[Int] = {
+  (x, y) match {
+    case (list, Nil) => list
+    case (Nil, list) => list
+    case (e1::rest1, e2::rest2) =>
+      if (e1 < e2) e1::merge(rest1, y)
+      else e2::merge(x, rest2)
+  }
+}
+
+val n1 = List(0, 2, 4, 6)
+val n2 = List(1, 3, 5, 7)
+merge(n1, n2)