Implement stack using two queues

Author: KarenOk

StackUsingQueues.js

@@ -0,0 +1,70 @@
+// Implement A Stack Using Two Queues
+
+class Stack {
+	constructor() {
+		this.queue1 = new Queue();
+		this.queue2 = new Queue();
+	}
+	push(val) {
+		this.queue1.enqueue(val);
+		return this;
+	}
+	pop() {
+		if (!this.queue1.size) return null;
+
+		while (this.queue1.size > 1) {
+			const value = this.queue1.dequeue();
+			this.queue2.enqueue(value);
+		}
+		let removed = this.queue1.dequeue();
+
+		// swap queue1 and queue2;
+		const temp = this.queue2;
+		this.queue2 = this.queue1;
+		this.queue1 = temp;
+
+		return removed;
+	}
+}
+
+// QUEUE AND NODE HAVE BEEN IMPLEMENTED FOR YOU
+
+class Node {
+	constructor(value) {
+		this.value = value;
+		this.next = null;
+	}
+}
+
+class Queue {
+	constructor() {
+		this.first = null;
+		this.last = null;
+		this.size = 0;
+	}
+	enqueue(data) {
+		var node = new Node(data);
+
+		if (!this.first) {
+			this.first = node;
+			this.last = node;
+		} else {
+			this.last.next = node;
+			this.last = node;
+		}
+
+		return ++this.size;
+	}
+
+	dequeue() {
+		if (!this.first) return null;
+
+		var temp = this.first;
+		if (this.first == this.last) {
+			this.last = null;
+		}
+		this.first = this.first.next;
+		this.size--;
+		return temp.value;
+	}
+}