Implement circular queue

Author: gopinav

Diff for: queue-circular.js

@@ -0,0 +1,84 @@
+class CircularQueue {
+  constructor(capacity) {
+    this.items = new Array(capacity);
+    this.rear = -1;
+    this.front = -1;
+    this.currentLength = 0;
+    this.capacity = capacity;
+  }
+
+  isFull() {
+    return this.currentLength === this.capacity;
+  }
+
+  isEmpty() {
+    return this.currentLength === 0;
+  }
+
+  size() {
+    return this.currentLength;
+  }
+
+  enqueue(item) {
+    if (!this.isFull()) {
+      this.rear = (this.rear + 1) % this.capacity;
+      this.items[this.rear] = item;
+      this.currentLength += 1;
+      if (this.front === -1) {
+        this.front = this.rear;
+      }
+    }
+  }
+
+  dequeue() {
+    if (this.isEmpty()) {
+      return null;
+    }
+    const item = this.items[this.front];
+    this.items[this.front] = null;
+    this.front = (this.front + 1) % this.capacity;
+    this.currentLength -= 1;
+    if (this.isEmpty()) {
+      this.front = -1;
+      this.rear = -1;
+    }
+    return item;
+  }
+
+  peek() {
+    if (!this.isEmpty()) {
+      return this.items[this.front];
+    }
+    return null;
+  }
+
+  print() {
+    if (this.isEmpty()) {
+      console.log("Queue is empty");
+    } else {
+      let i;
+      let str = "";
+      for (i = this.front; i !== this.rear; i = (i + 1) % this.capacity) {
+        str += this.items[i] + " ";
+      }
+      str += this.items[i];
+      console.log(str);
+    }
+  }
+}
+
+const queue = new CircularQueue(5);
+console.log(queue.isEmpty());
+queue.enqueue(10);
+queue.enqueue(20);
+queue.enqueue(30);
+queue.enqueue(40);
+queue.enqueue(50);
+console.log(queue.size());
+queue.print();
+console.log(queue.isFull());
+console.log(queue.dequeue());
+console.log(queue.peek());
+queue.print();
+queue.enqueue(60);
+queue.print();