diff --git a/src/main/scala/reductions/LineOfSight.scala b/src/main/scala/reductions/LineOfSight.scala
index 5d7ebfb..42649ab 100644
--- a/src/main/scala/reductions/LineOfSight.scala
+++ b/src/main/scala/reductions/LineOfSight.scala
@@ -41,13 +41,28 @@ case class Leaf(from: Int, until: Int, maxPrevious: Float) extends Tree
 object LineOfSight extends LineOfSightInterface {
 
   def lineOfSight(input: Array[Float], output: Array[Float]): Unit = {
-    ???
+    output(0) = 0
+    var i = 1
+    var maxSoFar = input(0);
+    while(i < input.length){
+      val tanOfAngle = input(i) / i;
+      if(tanOfAngle > maxSoFar) maxSoFar = tanOfAngle;
+      output(i) = maxSoFar;
+      i = i + 1
+    }
   }
 
   /** Traverses the specified part of the array and returns the maximum angle.
    */
   def upsweepSequential(input: Array[Float], from: Int, until: Int): Float = {
-    ???
+    def helper(i: Int, maxAngle: Float): Float = {
+      if (i < until) {
+          val newMaxAngle = scala.math.max(maxAngle, input(i) / i)
+          helper(i + 1, newMaxAngle)
+      }
+      else maxAngle
+  }
+    helper(from, -1)
   }
 
   /** Traverses the part of the array starting at `from` and until `end`, and
@@ -60,7 +75,15 @@ object LineOfSight extends LineOfSightInterface {
    */
   def upsweep(input: Array[Float], from: Int, end: Int,
     threshold: Int): Tree = {
-    ???
+      if(end-from <= threshold) Leaf(from, end, upsweepSequential(input, from , end))
+      else {
+        val mid = (end + from)/2
+        val (lt, rt) = parallel(
+          upsweep(input, from, mid, threshold),
+          upsweep(input, mid, end, threshold))
+
+        Node(lt, rt)
+      }
   }
 
   /** Traverses the part of the `input` array starting at `from` and until
@@ -69,7 +92,13 @@ object LineOfSight extends LineOfSightInterface {
    */
   def downsweepSequential(input: Array[Float], output: Array[Float],
     startingAngle: Float, from: Int, until: Int): Unit = {
-    ???
+      var maxSoFar = startingAngle
+      var i = from;
+      while(i < until){
+        maxSoFar = Math.max(input(i) / i, maxSoFar)
+        output(i) = maxSoFar
+        i = i + 1
+      }
   }
 
   /** Pushes the maximum angle in the prefix of the array to each leaf of the
@@ -78,12 +107,20 @@ object LineOfSight extends LineOfSightInterface {
    */
   def downsweep(input: Array[Float], output: Array[Float], startingAngle: Float,
     tree: Tree): Unit = {
-    ???
+      tree match{
+        case Leaf(from, until, maxPrevious) => downsweepSequential(input, output, startingAngle, from, until)
+        case Node(lt, rt) => parallel(
+          downsweep(input, output, startingAngle, lt),
+          downsweep(input, output, Math.max(startingAngle, lt.maxPrevious), rt)
+        )
+      }
   }
 
   /** Compute the line-of-sight in parallel. */
   def parLineOfSight(input: Array[Float], output: Array[Float],
     threshold: Int): Unit = {
-    ???
-  }
-}
+      val t = upsweep(input, 1, output.length, threshold)
+      downsweep(input, output, 0, t)
+      //output(0) = 0;
+    }
+  }
\ No newline at end of file
diff --git a/src/main/scala/reductions/ParallelCountChange.scala b/src/main/scala/reductions/ParallelCountChange.scala
index b5bd150..84d16dd 100644
--- a/src/main/scala/reductions/ParallelCountChange.scala
+++ b/src/main/scala/reductions/ParallelCountChange.scala
@@ -51,7 +51,14 @@ object ParallelCountChange extends ParallelCountChangeInterface {
    *  coins for the specified amount of money.
    */
   def countChange(money: Int, coins: List[Int]): Int = {
-    ???
+    if(money < 0) 0
+    else if(money == 0) 1
+    else{
+      coins match{
+        case Nil => 0
+        case c::cs => countChange(money-c, coins) + countChange(money, cs)
+      }
+    }
   }
 
   type Threshold = (Int, List[Int]) => Boolean
@@ -60,20 +67,30 @@ object ParallelCountChange extends ParallelCountChangeInterface {
    *  specified list of coins for the specified amount of money.
    */
   def parCountChange(money: Int, coins: List[Int], threshold: Threshold): Int = {
-    ???
+    if(threshold(money, coins) || money <= 0) countChange(money, coins)
+    else {
+      coins match{
+        case Nil => 0
+        case c::cs => {
+          val (a, b) = parallel(parCountChange(money-c, coins, threshold), parCountChange(money, cs, threshold))
+          a+b
+          }
+      }
+    }
+
   }
 
   /** Threshold heuristic based on the starting money. */
   def moneyThreshold(startingMoney: Int): Threshold =
-    ???
+    (x, _) => x <= (startingMoney * 2) / 3
 
   /** Threshold heuristic based on the total number of initial coins. */
   def totalCoinsThreshold(totalCoins: Int): Threshold =
-    ???
+    (_, cs) => cs.length <= (2 * totalCoins) / 3
 
 
   /** Threshold heuristic based on the starting money and the initial list of coins. */
   def combinedThreshold(startingMoney: Int, allCoins: List[Int]): Threshold = {
-    ???
+    (money, remCoins) => money * remCoins.length <= (startingMoney * allCoins.length)/2
   }
-}
+}
\ No newline at end of file
diff --git a/src/main/scala/reductions/ParallelParenthesesBalancing.scala b/src/main/scala/reductions/ParallelParenthesesBalancing.scala
index fcf1c36..a8c79af 100644
--- a/src/main/scala/reductions/ParallelParenthesesBalancing.scala
+++ b/src/main/scala/reductions/ParallelParenthesesBalancing.scala
@@ -40,25 +40,52 @@ object ParallelParenthesesBalancing extends ParallelParenthesesBalancingInterfac
   /** Returns `true` iff the parentheses in the input `chars` are balanced.
    */
   def balance(chars: Array[Char]): Boolean = {
-    ???
+    var i = 0;
+    var count = 0;
+    while(i < chars.length){
+      if(chars(i) == '(') count = count + 1
+      else if(chars(i) == ')') count = count - 1
+
+      if(count < 0) return false
+      i = i + 1
+    }
+    if(count != 0) return false else true
   }
 
   /** Returns `true` iff the parentheses in the input `chars` are balanced.
    */
   def parBalance(chars: Array[Char], threshold: Int): Boolean = {
 
-    def traverse(idx: Int, until: Int, arg1: Int, arg2: Int) /*: ???*/ = {
-      ???
+    def traverse(idx: Int, until: Int, unmatchedOpening: Int, unmatchedClosing: Int) : (Int, Int) = {
+      if(idx >= until) (unmatchedOpening, unmatchedClosing)
+      else chars(idx) match {
+        case '(' => traverse(idx+1, until, unmatchedOpening + 1, unmatchedClosing)
+        case ')' =>
+          if(unmatchedOpening != 0) traverse(idx+1, until, unmatchedOpening - 1, unmatchedClosing)
+          else traverse(idx+1, until, unmatchedOpening, unmatchedClosing+1)
+        case _ => traverse(idx+1, until, unmatchedOpening, unmatchedClosing)
+      }
     }
 
-    def reduce(from: Int, until: Int) /*: ???*/ = {
-      ???
+    def reduce(from: Int, until: Int) : (Int,Int) = {
+
+      if(until - from <= threshold) traverse(from, until, 0, 0)
+      else{
+        val mid = (from + until) / 2
+        val ((auo, auc), (buo, buc)) = parallel(
+          reduce(from, mid),
+          reduce(mid, until)
+        )
+
+        val canMatch = Math.min(auo, buc)
+        (auo+buo-canMatch, auc + buc - canMatch)
+      }
     }
 
-    reduce(0, chars.length) == ???
+    reduce(0, chars.length) == (0, 0)
   }
 
   // For those who want more:
   // Prove that your reduction operator is associative!
 
-}
+}
\ No newline at end of file