From 76a82e293af145c898201242307ff9f31cc65aad Mon Sep 17 00:00:00 2001
From: Sandeepan-Das <sandeepandas2000@gmail.com>
Date: Fri, 2 Oct 2020 22:15:29 +0530
Subject: [PATCH] Add Circular Queue

---
 Data-Structures/Queue/CircularQueue.js | 108 +++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 Data-Structures/Queue/CircularQueue.js

diff --git a/Data-Structures/Queue/CircularQueue.js b/Data-Structures/Queue/CircularQueue.js
new file mode 100644
index 000000000..72ae57272
--- /dev/null
+++ b/Data-Structures/Queue/CircularQueue.js
@@ -0,0 +1,108 @@
+// Circular Queues offer a quick to store FIFO data with a maximum size.
+// Conserves memory as we only store up to our capacity
+// It is opposed to a queue which could continue to grow if input outpaces output
+// Doesn’t use dynamic memory so No memory leaks
+
+class CircularQueue {
+  constructor (maxLength) {
+    this.queue = []
+    this.front = 0
+    this.rear = 0
+    this.maxLength = maxLength
+  }
+
+  // ADD ELEMENTS TO QUEUE
+  enqueue (value) {
+    if (this.checkOverflow()) return
+    if (this.checkEmpty()) {
+      this.front += 1
+      this.rear += 1
+    } else {
+      if (this.rear === this.maxLength) {
+        this.rear = 1
+      } else this.rear += 1
+    }
+    this.queue[this.rear] = value
+  }
+
+  // REMOVES ELEMENTS
+  dequeue () {
+    if (this.checkEmpty()) {
+      console.log('UNDERFLOW')
+      return
+    }
+    const y = this.queue[this.front]
+    this.queue[this.front] = '*'
+    if (this.checkSingleelement()) {
+
+    } else {
+      if (this.front === this.maxLength) this.front = 1
+      else {
+        this.front += 1
+      }
+    }
+
+    return y // Returns the removed element and replaces it with a star
+  }
+
+  // checks if the queue is empty or not
+  checkEmpty () {
+    if (this.front === 0 && this.rear === 0) {
+      return true
+    }
+  }
+
+  checkSingleelement () {
+    if (this.front === this.rear && this.rear !== 0) {
+      this.front = this.rear = 0
+      return true
+    }
+  }
+
+  // Checks if max capacity of queue has been reached or not
+  checkOverflow () {
+    if ((this.front === 1 && this.rear === this.maxLength) || (this.front === this.rear + 1)) {
+      console.log('CIRCULAR QUEUE OVERFLOW')
+      return true
+    }
+  }
+
+  // Prints the entire array
+  display () {
+    for (let index = 1; index < this.queue.length; index++) {
+      console.log(this.queue[index])
+    }
+  }
+
+  // Displays the length of queue
+  length () {
+    return this.queue.length - 1
+  }
+
+  // Display the top most value of queue
+  peek () {
+    return this.queue[this.front]
+  }
+}
+
+function main () {
+  // Star represents blank space
+  const queue = new CircularQueue(6) // Enter Max Length
+  queue.enqueue(1)
+  queue.enqueue(15)
+  queue.enqueue(176)
+  queue.enqueue(59)
+  queue.enqueue(3)
+  queue.enqueue(55)
+
+  queue.display()
+
+  queue.dequeue()
+  queue.dequeue()
+  queue.dequeue()
+  queue.display()
+
+  console.log(queue.peek())
+}
+
+main()