Implemented queue (Closes #4)

The following data structures have been implemented: Array, Hash Table, Stack, Queue, Binary Search Tree. All are available for import.

Author: CoffeelessProgrammer

Data-Structures/README.md

@@ -3,8 +3,8 @@
 ## Core
 - [X] Arrays
 - [X] Hash Tables
-- [ ] Stacks
-- [ ] Queues
+- [X] Stacks
+- [X] Queues
 - [ ] Linked Lists
 - [X] Trees
   - [X] Binary Search Tree (BST)

Data-Structures/Sequential/Queue.ts

@@ -0,0 +1,112 @@
+import Node from '../Linked-Lists/NodeLL.ts';
+
+
+export default class Queue<T> {
+  private last: Node<T> | null;
+  private first: Node<T>| null;
+  private length: number;
+
+  constructor() {
+    this.last = null;
+    this.first = null;
+    this.length = 0;
+  }
+
+  public getLength(): number {
+    return this.length;
+  }
+
+  public peek(): T | null {
+    return this.first?.getValue() || null;
+  }
+
+  public enqueue(value: T): boolean {
+    const newNode = new Node(value);
+
+    if (!this.last) {                         // If empty queue, initialize
+      this.first = newNode;
+      this.last = newNode;
+    }
+    else {
+      this.last.setNext(newNode);
+      this.last = this.last.getNext();
+    }
+
+    ++this.length;
+    return true;
+  }
+
+  public dequeue(): T | null {
+    if (!this.first) return null;             // Edge case: Empty queue
+
+    if (this.length === 1) {                  // Edge case: Queue has 1 element, so a dequeue should reset the queue's state
+      this.last = null;                       // Challenge: What is the state of each 'class field' after a dequeue when 1 element was remaining?
+    }
+
+    const value = this.first.getValue();
+    this.first = this.first.getNext();
+
+    --this.length;
+    return value;
+  }
+}
+
+function printQueue(queue: Queue<any>) {
+  console.log(JSON.stringify(queue));
+}
+
+function printPeekQueue(queue: Queue<any>) {
+  console.log('Peeking... Found', JSON.stringify(queue.peek()));
+}
+
+function printDequeue(queue: Queue<any>) {
+  console.log('Dequeued:', JSON.stringify(queue.dequeue()));
+}
+
+
+//---------------------------------------------------------------------
+// ----------                 MAIN PROGRAM                   ----------
+//---------------------------------------------------------------------
+if (import.meta.main) {
+
+  const ATLA = new Queue<string>();
+
+  printPeekQueue(ATLA);
+  ATLA.enqueue('Sokka');
+  ATLA.enqueue('Katara');
+  printPeekQueue(ATLA);
+  ATLA.enqueue('Aang');
+  ATLA.enqueue('Appa');
+
+  printQueue(ATLA);
+
+  printDequeue(ATLA);
+  printDequeue(ATLA);
+  printDequeue(ATLA);
+
+  printQueue(ATLA);
+  
+  printDequeue(ATLA);
+
+  printQueue(ATLA);
+
+  ATLA.enqueue('Zuko');
+  ATLA.enqueue('Iroh');
+
+  printQueue(ATLA);
+
+  // RUN: deno run Data-Structures/Sequential/Queue.ts
+}
+
+
+// --------------------------- Terminal Output: ---------------------------
+// Peeking... Found null
+// Peeking... Found "Sokka"
+// {"last":{"value":"Appa","next":null},"first":{"value":"Sokka","next":{"value":"Katara","next":{"value":"Aang","next":{"value":"Appa","next":null}}}},"length":4}       
+// Dequeued: "Sokka"
+// Dequeued: "Katara"
+// Dequeued: "Aang"
+// {"last":{"value":"Appa","next":null},"first":{"value":"Appa","next":null},"length":1}
+// Dequeued: "Appa"
+// {"last":null,"first":null,"length":0}
+// {"last":{"value":"Iroh","next":null},"first":{"value":"Zuko","next":{"value":"Iroh","next":null}},"length":2}

Data-Structures/Sequential/Stack.ts

@@ -73,4 +73,17 @@ if (import.meta.main) {
   printStack(ATLA);
 
   // RUN: deno run Data-Structures/Sequential/Stack.ts
-}
+}
+
+
+// --------------------------- Terminal Output: ---------------------------
+// Peeking... Found null
+// Peeking... Found Katara
+// {"length":4,"values":["Sokka","Katara","Aang","Appa"]}
+// Popped: Appa
+// {"length":3,"values":["Sokka","Katara","Aang",null]}
+// Popped: Aang
+// Popped: Katara
+// Popped: Sokka
+// {"length":0,"values":[null,null,null,null]}
+// {"length":2,"values":["Zuko","Iroh",null,null]}

Data-Structures/Sequential/StackLL.ts

@@ -106,4 +106,17 @@ if (import.meta.main) {
   printStack(ATLA);
 
   // RUN: deno run Data-Structures/Sequential/StackLL.ts
-}
+}
+
+
+// --------------------------- Terminal Output: ---------------------------
+// Peeking: null
+// Peeking: Katara
+// {"top":{"value":"Appa","next":{"value":"Aang","next":{"value":"Katara","next":{"value":"Sokka","next":null}}}},"bottom":{"value":"Sokka","next":null},"length":4}      
+// Popped: Appa
+// {"top":{"value":"Aang","next":{"value":"Katara","next":{"value":"Sokka","next":null}}},"bottom":{"value":"Sokka","next":null},"length":3}
+// Popped: Aang
+// Popped: Katara
+// Popped: Sokka
+// {"top":null,"bottom":null,"length":0}
+// {"top":{"value":"Iroh","next":{"value":"Zuko","next":null}},"bottom":{"value":"Zuko","next":null},"length":2}

README.md

@@ -10,8 +10,8 @@
 ### Data Structures
 - [X] Arrays
 - [X] Hash Tables
-- [ ] Stacks
-- [ ] Queues
+- [X] Stacks
+- [X] Queues
 - [ ] Linked Lists
 - [X] Trees
 - [ ] Graphs