Added Queue

RashikAnsar · RashikAnsar · commit 0d604bc7096b · 2018-10-24T10:27:19.000+05:30
diff --git a/data-structures/queue.js b/data-structures/queue.js
@@ -0,0 +1,68 @@
+/**
+ * @author Rashik Ansar
+ *
+ * Implementation of Queue Data structure
+ * Queue follows FIFO (First In First Out) Principle
+ */
+
+class Node {
+  constructor(data) {
+    this.data = data;
+    this.next = null;
+  }
+}
+
+class Queue {
+  constructor() {
+    this.first = null;
+    this.last = null;
+    this.size = 0;
+  }
+
+  /**
+   * Adding data to the end of queue
+   * @param {*} data Data to add in the queue
+   * @returns {Queue} Returns the queue after adding new data
+   */
+  enqueue(data) {
+    let newNode = new Node(data);
+    if (!this.first) {
+      this.first = newNode;
+      this.last = newNode;
+    } else {
+      this.last.next = newNode;
+      this.last = newNode;
+    }
+    this.size++;
+    return this;
+  }
+
+  /**
+   * Removing data from the beginning of the queue
+   * @returns Data that is removing from queue
+   */
+  dequeue() {
+    if (!this.first) {
+      throw Error(
+        'UNDERFLOW::: The queue is empty, there is nothing to remove'
+      );
+    }
+    let temp = this.first;
+    if (this.first === this.last) {
+      this.last = null;
+    }
+    this.first = this.first.next;
+    this.size--;
+    return temp.data;
+  }
+
+  /**
+   * @returns First element in the queue
+   */
+  peek() {
+    if (!this.first) {
+      throw Error('Stack is empty');
+    }
+    return this.first.data;
+  }
+}
