Implementing Stack and Queue in Kotlin (fixed)

contents/stacks_and_queues/code/kotlin/Queue.kt

@@ -0,0 +1,33 @@
+class Queue<T> {
+    private val list = mutableListOf<T>()
+
+    fun enqueue(item: T) {
+        list.add(item)
+    }
+
+    fun dequeue(): T? {
+        return if (list.isEmpty()) {
+            null
+        } else list.removeAt(0)
+    }
+
+    fun front(): T? {
+        return if (list.isEmpty()) {
+            null
+        } else list[0]
+    }
+
+    fun size(): Int = list.size
+}
+
+fun main(args: Array<String>) {
+    val queue = Queue<Int>()
+    queue.enqueue(1)
+    queue.enqueue(2)
+    queue.enqueue(3)
+
+    println("Front: ${queue.front()}")
+    println(queue.dequeue())
+    println("Size: ${queue.size()}")
+    println(queue.dequeue())
+}

contents/stacks_and_queues/code/kotlin/Stack.kt

@@ -0,0 +1,33 @@
+class Stack<T> {
+    private val list = mutableListOf<T>()
+
+    fun push(item: T) {
+        list.add(item)
+    }
+
+    fun pop(): T? {
+        return if (list.isEmpty()) {
+            null
+        } else list.removeAt(list.size - 1)
+    }
+
+    fun size(): Int = list.size
+
+    fun top(): T? {
+        return if (list.isEmpty()) {
+            null
+        } else list[list.size - 1]
+    }
+}
+
+fun main(args: Array<String>) {
+    val stack = Stack<Int>()
+    stack.push(1)
+    stack.push(2)
+    stack.push(3)
+
+    println("Top: ${stack.top()}")
+    println(stack.pop())
+    println("Size: ${stack.size()}")
+    println(stack.pop())
+}

contents/stacks_and_queues/stacks_and_queues.md

@@ -28,6 +28,8 @@ Here is a simple implementation of a stack:
 [import, lang:"rust"](code/rust/Stack.rs)
 {% sample lang="python" %}
 [import, lang:"python"](code/python/stack.py)
+{% sample lang="kotlin" %}
+[import, lang:"kotlin"](code/kotlin/Stack.kt)
 {% endmethod %}
 
 Here is a simple implementation of a queue:
@@ -42,6 +44,8 @@ Here is a simple implementation of a queue:
 [import, lang:"rust" ](code/rust/Queue.rs)
 {% sample lang="python" %}
 [import, lang:"python"](code/python/queue.py)
+{% sample lang="kotlin" %}
+[import, lang:"kotlin"](code/kotlin/Queue.kt)
 {% endmethod %}
 
 ## License