Fixed the sum and max functions of Lists

src/main/scala/example/Lists.scala

@@ -22,7 +22,7 @@ object Lists {
    * @param xs A list of natural numbers
    * @return The sum of all elements in `xs`
    */
-  def sum(xs: List[Int]): Int = ???
+  def sum(xs: List[Int]): Int = if xs.isEmpty then 0 else xs.head + sum(xs.tail)
 
   /**
    * This method returns the largest element in a list of integers. If the
@@ -37,5 +37,9 @@ object Lists {
    * @return The largest element in `xs`
    * @throws java.util.NoSuchElementException if `xs` is an empty list
    */
-  def max(xs: List[Int]): Int = ???
+  def max(xs: List[Int]): Int = if xs.isEmpty 
+    then throw new NoSuchElementException 
+    else if xs.size == 1 then xs.head else compare(max(xs.tail), xs.head)
+
+  def compare(x: Int, y: Int): Int = if x >= y then x else y 
 }

src/test/scala/example/ListsSuite.scala

@@ -24,7 +24,7 @@ class ListsSuite {
     assert(1 + 1 == 2)
 
   @Test def `one plus one is three (0pts)?`: Unit =
-    assert(1 + 1 == 3) // This assertion fails! Go ahead and fix it.
+    assert(1 + 1 != 3) // This assertion fails! Go ahead and fix it.
 
   /**
    * One problem with the previous (failing) test is that JUnit will
@@ -48,7 +48,7 @@ class ListsSuite {
    * when writing tests.
    */
   @Test def `details why one plus one is not three (0pts)`: Unit =
-    Assert.assertEquals(3, 1 + 1) // Fix me, please!
+    Assert.assertEquals(2, 1 + 1) // Fix me, please!
 
   /**
    * Exceptional behavior of a methods can be tested using a try/catch