Queue implementation

build.gradle

@@ -14,6 +14,8 @@ repositories {
 
 dependencies {
  implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
+ implementation 'org.assertj:assertj-core:3.21.0'
+
  testCompile group: 'junit', name: 'junit', version: '4.12'
 }
 

src/main/kotlin/datastructures/queues/Queue.kt

@@ -0,0 +1,74 @@
+package datastructures
+
+const val DEFAULT_CAPACITY = 10
+
+/**
+ * This is an implementation of a Queue
+ * that uses an array as primary structure
+ *
+ * A queue data structure functions the same as a real world queue. The elements
+ * that are added first are the first to be removed. New elements are added to
+ * the back/rear of the queue.
+ */
+class Queue (size: Int?) {
+
+ private val maxCapacity = size ?: DEFAULT_CAPACITY
+
+ private var itemsCount = 0
+
+ private val queue = IntArray(maxCapacity)
+
+ private var last = -1
+
+ private var first = 0
+
+ /**
+ * @param value is an integer that will be inserted into the queue
+ * @returns false if the queue is full and true if the item was inserted
+ */
+ fun enqueue(value: Int): Boolean {
+ if (isFull()) return false
+
+ itemsCount++
+
+ last = (last + 1) % maxCapacity
+ queue[last] = value
+
+ return true
+ }
+
+ /**
+ * @returns the first item inserted into the queue, and null if it's empty
+ */
+ fun dequeue(): Int? {
+ if (isEmpty()) {
+ return null
+ }
+
+ val itemToReturn = queue[first]
+ first = (first + 1) % maxCapacity
+
+ itemsCount--
+
+ return itemToReturn
+ }
+
+ /**
+ * @returns the first item inserted into the queue as string
+ */
+ fun peekFirst(): String = queue[first].toString()
+
+ /**
+ * @returns the last item inserted into the queue as string
+ */
+ fun peekLast(): String = queue[last].toString()
+
+ /**
+ * @returns the amount of itens inside the queue
+ */
+ fun getSize(): Int = itemsCount
+
+ private fun isFull(): Boolean = itemsCount == maxCapacity
+
+ private fun isEmpty(): Boolean = itemsCount == 0
+}

src/test/kotlin/datastructures/queues/QueueTest.kt

@@ -0,0 +1,59 @@
+package datastructures.queues
+import org.assertj.core.api.Assertions.assertThat
+import datastructures.Queue
+
+import org.junit.Test
+
+internal class QueueTest {
+
+ @Test
+ fun `#enqueue must return true queue is not full`() {
+ val valueToInsert = 1
+
+ val newQueue = Queue(10)
+ val returnedValue = newQueue.enqueue(valueToInsert)
+
+ assertThat(returnedValue).isTrue()
+ }
+
+ @Test
+ fun `#enqueue must return false queue is full`() {
+ val valueToInsert = 20
+ val queueSize = 4
+ val newQueue = Queue(queueSize)
+
+ for(i in 0 until queueSize + 1) {
+ newQueue.enqueue(i)
+ }
+
+ val returnedValue = newQueue.enqueue(valueToInsert)
+
+ assertThat(returnedValue).isFalse()
+ }
+
+ @Test
+ fun `#dequeue must return null when queue is empty`() {
+ val queueSize = 2
+ val newQueue = Queue(queueSize)
+
+ val returnedValue = newQueue.dequeue()
+
+ assertThat(returnedValue).isNull()
+ }
+
+ @Test
+ fun `#dequeue must return a value when queue is not empty`() {
+ val valueToInsert = 20
+ val queueSize = 4
+ val newQueue = Queue(queueSize)
+
+ for(i in 0 until queueSize + 1) {
+ newQueue.enqueue(i)
+ }
+
+ val returnedValue = newQueue.dequeue()
+
+ assertThat(returnedValue).isNotNull()
+ assertThat(returnedValue).isEqualTo(0)
+ }
+}