From a8c24e908c65cea78bdab10ece0045b3c3501482 Mon Sep 17 00:00:00 2001
From: Samson Alajede <ajesamson@yahoo.com>
Date: Thu, 17 Oct 2024 17:30:52 +0100
Subject: [PATCH] Added reverse queue implementation in javascript

---
 .../src/queue/reverse_queue/reverse_queue.js  | 121 ++++++++++++++++++
 1 file changed, 121 insertions(+)
 create mode 100644 code/data_structures/src/queue/reverse_queue/reverse_queue.js

diff --git a/code/data_structures/src/queue/reverse_queue/reverse_queue.js b/code/data_structures/src/queue/reverse_queue/reverse_queue.js
new file mode 100644
index 0000000000..776c2fc222
--- /dev/null
+++ b/code/data_structures/src/queue/reverse_queue/reverse_queue.js
@@ -0,0 +1,121 @@
+/**
+ * Part of Cosmos by OpenGenus Foundation
+ */
+
+function Queue() {
+  this.queue = [];
+  this.stack = [];
+  this.frontEl = null;
+  this.total = 0;
+
+  this.enqueue = function (el) {
+    if (this.total == 0) {
+      this.frontEl = el;
+    }
+
+    this.queue.push(el);
+    this.total++;
+  };
+
+  this.dequeue = function () {
+    // Confirm if stack is empty and return
+    if (this.total == 0) {
+      console.log("The queue is empty!");
+
+      return;
+    }
+
+    // Move all queue entries to stack if stack is empty
+    if (this.stack.length == 0) {
+      while (this.queue.length > 0) {
+        this.stack.push(this.queue.pop());
+      }
+    }
+
+    this.total--;
+    // Return the topmost element
+    return this.stack.pop();
+  };
+
+  this.size = function () {
+    return this.total;
+  };
+
+  this.front = function () {
+    if (this.stack.length > 0) {
+      return this.stack[this.stack.length - 1];
+    }
+
+    return this.frontEl;
+  };
+
+  this.reverse = function () {
+    if (this.total == 0) {
+      console.log("The queue is empty");
+
+      return;
+    }
+
+    this.stack.reverse();
+    this.queue.reverse();
+    while (this.queue.length > 0) {
+      this.stack.push(this.queue.pop());
+    }
+
+    this.frontEl = this.stack[this.stack.length - 1];
+  };
+
+  this.print = function () {
+    if (this.total == 0) {
+      console.log(this.queue);
+      return;
+    }
+
+    let output = [];
+    for (let i = this.stack.length - 1; i >= 0; --i) {
+      output.push(this.stack[i]);
+    }
+    for (let q of this.queue) {
+      output.push(q);
+    }
+
+    console.log(output);
+  };
+}
+
+const queue = new Queue();
+const items = [1, 2, 3, 4];
+for (let i of items) {
+  queue.enqueue(i);
+}
+console.log("\nCurrent queue");
+console.log("===============");
+queue.print();
+
+console.log("\nCurrent queue front");
+console.log("===============");
+console.log(queue.front());
+
+const el = queue.dequeue();
+console.log("\nRemoved element:");
+console.log("===============");
+console.log(el);
+
+console.log("\nCurrent queue");
+console.log("===============");
+queue.print();
+
+queue.enqueue(5);
+queue.enqueue(6);
+console.log("\nUpdated queue");
+console.log("===============");
+queue.print();
+
+console.log("\nReversed queue");
+console.log("===============");
+queue.reverse();
+queue.print();
+
+console.log("\nReversed queue front");
+console.log("===============");
+console.log(queue.front());