Add Queue class

Signed-off-by: Darko Draskovic <[email protected]>

src/index.js

@@ -1,3 +1,3 @@
-import { test } from './stack.js'
+import { test } from './queue.js'
 
 test()

src/queue.js

@@ -0,0 +1,123 @@
+import { Stack } from './stack.js'
+
+class Node {
+ constructor(value) {
+ this.value = value;
+ this.next = null;
+ }
+}
+
+class Queue {
+ constructor() {
+ this.first = null;
+ this.last = null;
+ this.length = 0;
+ }
+ peek() {
+ return this.first;
+ }
+ enqueue(value) {
+ if (!this.length) {
+ this.first = this.last = new Node(value);
+ } else {
+ this.last.next = new Node(value);
+ this.last = this.last.next;
+ }
+ this.length++;
+ }
+ dequeue() {
+ if (!this.length) return null;
+
+ const first = this.first;
+ this.first = this.first.next;
+ this.length--;
+
+ if (!this.length) this.last = null;
+
+ return first;
+ }
+ array() {
+ const arr = [];
+ let current = this.first;
+ while(current) {
+ arr.push(current.value);
+ current = current.next;
+ }
+ return arr;
+ }
+}
+
+class QueueStack {
+ constructor() {
+ this.stack = new Stack(); 
+ }
+ enqueue(value) {
+ this.stack.push(value);
+ }
+ dequeue() {
+ if (this.stack.isEmpty()) return null;
+
+ const temp = new Stack();
+ while (this.stack.length > 1) {
+ temp.push(this.stack.pop().value);
+ }
+ const first = this.stack.pop();
+ while (temp.length > 0) {
+ this.stack.push(temp.pop().value);
+ }
+ return first;
+ }
+ peek() {
+ // TODO:
+ }
+ isEmpty() {
+ return this.stack.isEmpty();
+ }
+ array() {
+ return this.stack.array();
+ }
+ get length() {
+ return this.stack.length;
+ }
+}
+
+export function test() {
+ // const queue = new Queue();
+ const queue = new QueueStack();
+ const n = 10;
+ for (let i = 0; i < n; i++) {
+ queue.enqueue(i);
+ }
+ console.log("len: " + queue.length);
+ console.log("queue: "+ queue.array());
+
+ console.log("\ndequeue 1 item");
+ queue.dequeue()
+ console.log("len: " + queue.length);
+ console.log("queue: "+ queue.array());
+
+ console.log("\ndequeue everything except last");
+ while (queue.length > 1) {
+ queue.dequeue();
+ }
+ console.log("len: " + queue.length);
+ console.log("queue: "+ queue.array());
+
+ console.log("\ndequeue last");
+ queue.dequeue()
+ console.log("len: " + queue.length);
+ console.log("queue: "+ queue.array());
+
+ console.log("\ndequeue empty queue");
+ queue.dequeue()
+ console.log("len: " + queue.length);
+ console.log("queue: "+ queue.array());
+
+ console.log("\nenqueue " + n + " items");
+ queue.enqueue(0);
+ for (let i = 1; i < 10; i++) {
+ queue.enqueue(i);
+ }
+ console.log("len: " + queue.length);
+ console.log("queue: "+ queue.array());
+}

src/stack.js

@@ -1,7 +1,7 @@
 class Node {
  constructor(value) {
  this.value = value;
- this.next = null;
+ this.prev = null;
  }
 }
 
@@ -15,53 +15,79 @@ export class Stack {
  return this.top;
  }
  push(value) {
+ const newNode = new Node(value);
  if (this.isEmpty()) {
- this.top = new Node(value);
- this.bottom = this.top;
+ this.bottom = this.top = newNode;
  } else {
- this.top.next = new Node(value);
- this.top = this.top.next;
+ const temp = this.top;
+ this.top = newNode;
+ newNode.prev = temp;
  }
  this.length++;
  return this;
  }
  pop() {
  if (this.isEmpty()) return null;
 
- if (this.length === 1) {
- this.bottom = this.top = null;
- } else {
- const current = this.traverse(this.length-2);
- this.top = current;
- this.top.next = null;
- }
-
+ const top = this.top;
+
+ this.top = this.top.prev;
  this.length--;
- return this;
+ if (this.isEmpty) this.bottom = null;
+
+ return top;
  }
  isEmpty() {
  return !this.length;
  }
- traverse(index) {
- let current = this.bottom;
- for (let i = 0; i < index; i++) {
- current = current.next;
- }
- return current;
- }
  array() {
  const arr = [];
- let current = this.bottom;
+ let current = this.top;
  while (current) {
  arr.push(current.value);
- current = current.next;
+ current = current.prev;
  }
- return arr;
+ return arr.reverse();
+ }
+}
+
+export class StackArray {
+ constructor() {
+ this.arr = [];
+ }
+ peek() {
+ // if (!this.arr.length) return null;
+ return this.arr[this.arr.length-1];
+ }
+ push(value) {
+ this.arr.push(value);
+ return this;
+ }
+ pop() {
+ // if (!this.arr.length) return null;
+ return this.arr.pop();
+ }
+ isEmpty() {
+ return !this.arr.length;
+ }
+
+ array() {
+ return this.arr;
+ }
+ get length() {
+ return this.arr.length;
+ }
+ get bottom() {
+ return this.arr[0]
+ }
+ get top() {
+ return this.arr[this.arr.length-1];
  }
 }
 
 export function test() {
- const stack = new Stack();
+ // const stack = new Stack();
+ const stack = new StackArray();
  const n = 10;
  for (let i = 0; i < n; i++) {
  stack.push(i);