update: reverse-first-k elements of a queue

Author: ashokdey

src/_DataStructures_/Queue/reverse-first-k/index.js

@@ -0,0 +1,48 @@
+// eslint-disable-next-line no-unused-vars
+const Queue = require('../index');
+const Stack = require('../../Stack');
+
+function reverseFirstKElelments(q, k) {
+  const s = new Stack();
+
+  // push all the k elements ot the stack
+  for (let i = 0; i < k; i += 1) {
+    s.push(q.dequeue());
+  }
+
+  // push the stack items to the queue
+  for (let i = 0; i < k; i += 1) {
+    q.enqueue(s.pop());
+  }
+
+  // empty the queue and push the same queue
+  const remaining = q.length() - k;
+  for (let i = 0; i < remaining; i += 1) {
+    q.enqueue(q.dequeue());
+  }
+
+  // return the queue
+  return q;
+}
+
+module.exports = reverseFirstKElelments;
+
+// let q = new Queue();
+
+// q.enqueue(1);
+// q.enqueue(2);
+// q.enqueue(3);
+// q.enqueue(4);
+// q.enqueue(5);
+// q.enqueue(6);
+// q.enqueue(7);
+// q.enqueue(8);
+// q.enqueue(9);
+
+// q = reverseFirstKElelments(q, 4);
+
+// const arr = [];
+// while (q.length()) {
+//   arr.push(q.dequeue());
+// }
+// console.log(arr);

src/_DataStructures_/Stack/index.js

@@ -15,8 +15,10 @@ class Stack {
   peek() {
     return this.data[this.data.length - 1];
   }
-  isEmpty(){ //check if stack is empty
-    return this.data.length==0;
+
+  isEmpty() {
+    // check if stack is empty
+    return this.data.length === 0;
   }
 }