Fix: Remove item from empty queue/stack

Author: igorwojda

src/test/kotlin/com/igorwojda/queue/basic/challenge.kt

@@ -11,9 +11,9 @@ private class Queue<E> {
         TODO("not implemented")
     }
 
-    fun remove(): E? = TODO("not implemented")
+    fun remove(): E = TODO("not implemented")
 
-    fun peek(): E? = TODO("not implemented")
+    fun peek(): E = TODO("not implemented")
 
     fun isEmpty(): Boolean {
         TODO("not implemented")
@@ -104,4 +104,13 @@ private class Test {
             size shouldBeEqualTo 0
         }
     }
+
+    @Test
+    fun `remove item from empty queue`() {
+        Queue<Int>().apply {
+            remove()
+
+            size shouldBeEqualTo 0
+        }
+    }
 }

src/test/kotlin/com/igorwojda/queue/basic/solution.kt

@@ -31,6 +31,8 @@ private object Solution1 {
         }
 
         fun remove(): E? {
+            if (size == 0) return null
+
             val node = first
             first = node?.next
             size--

src/test/kotlin/com/igorwojda/stack/basic/challenge.kt

@@ -123,4 +123,13 @@ private class Test {
             size shouldBeEqualTo 0
         }
     }
+
+    @Test
+    fun `remove item from empty stack`() {
+        Stack<Char>().apply {
+            remove()
+
+            size shouldBeEqualTo 0
+        }
+    }
 }

src/test/kotlin/com/igorwojda/stack/basic/solution.kt

@@ -30,6 +30,8 @@ private object Solution1 {
         }
 
         fun remove(): E? {
+            if (size == 0) return null
+
             val node = first
             first = first?.next
             size--