Stack and Queue implementation in Crystal

contents/stacks_and_queues/code/crystal/queue.cr

@@ -0,0 +1,44 @@
+class Queue(T)
+  # The items in the queue.
+  @queue : Array(T)
+
+  # Creates a new empty queue.
+  def initialize
+    @queue = Array(T).new
+  end
+
+  # Pushes the given *item* onto the queue and returns the size of the queue.
+  def enqueue(item : T)
+    @queue << item
+    self.size
+  end
+
+  # Removes the first item in the queue (at index 0).
+  def dequeue : T
+    @queue.shift
+  end
+
+  # Returns the first item in the queue (at index 0).
+  def front : T
+    @queue[0]
+  end
+
+  # Returns the number of items in the queue.
+  def size : Int32
+    @queue.size
+  end
+end
+
+def queue_example
+  queue = Queue(Int32).new
+
+  queue.enqueue(4)
+  queue.enqueue(5)
+  queue.enqueue(9)
+
+  puts queue.dequeue
+  puts queue.size
+  puts queue.front
+end
+
+queue_example

contents/stacks_and_queues/code/crystal/stack.cr

@@ -0,0 +1,44 @@
+class Stack(T)
+  # The items in the stack.
+  @stack : Array(T)
+
+  # Creates a new empty stack.
+  def initialize
+    @stack = Array(T).new
+  end
+
+  # Pushes the given *item* onto the stack and returns the size of the stack.
+  def push(item : T)
+    @stack << item
+    self.size
+  end
+
+  # Remove the last item from the stack.
+  def pop() : T
+    @stack.pop
+  end
+
+  # Returns the number of items in the stack.
+  def size : Int32
+    @stack.size
+  end
+
+  # Returns the last item push onto the stack.
+  def top : T
+    @stack[-1]
+  end
+end
+
+def stack_example
+  stack = Stack(Int32).new
+
+  stack.push(4)
+  stack.push(5)
+  stack.push(9)
+
+  puts stack.pop
+  puts stack.size
+  puts stack.top
+end
+
+stack_example

contents/stacks_and_queues/stacks_and_queues.md

@@ -16,12 +16,16 @@ The notation for this depends on the language you are using. Queues, for example
 ## Example Code
 Here is a simple implementation of a stack:
 {% method %}
+{% sample lang="crystal" %}
+[import, lang:"crystal"](code/crystal/stack.cr)
 {% sample lang="ts" %}
 [import, lang:"typescript"](code/typescript/stack.ts)
 {% endmethod %}
 
 Here is a simple implementation of a queue:
 {% method %}
+{% sample lang="crystal" %}
+[import, lang:"crystal"](code/crystal/queue.cr)
 {% sample lang="ts" %}
 [import, lang:"typescript"](code/typescript/queue.ts)
 {% endmethod %}