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Commit 7ca7bd9

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Merge pull request knaxus#81 from knaxus/problems
Problems involving Queues
2 parents 5bec3a5 + 75b69be commit 7ca7bd9

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‎README.md‎

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@@ -30,10 +30,12 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
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- [Remove Consecutive Repeated Digits](src/_DataStructures_/Stack/remove-consecutive-repeated-digits)
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- [Implement 2 Stacks using Single Array](src/_DataStructures_/Stack/2-stacks-using1-array)
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- [Queue](src/_DataStructures_/Queue)
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- [Weave](src/_DataStructures_/Queue/weave)
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- [Reverse First K Elements of a Queue](src/_DataStructures_/Queue/reverse-first-k)
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- [Generate all Binary Numbers from 1 to N](src/_DataStructures_/Queue/generate-binary-number)
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- [Queue using Stack](src/_DataStructures_/Queue/queue-using-stack)
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- [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
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const Queue = require('../index');
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function generateBinaryNumber(n) {
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const result = [];
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const q = new Queue();
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// add `1` to the queue
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q.enqueue('1');
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// iterate till the given number
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for (let i = 0; i < n; i += 1) {
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// push the item in the queue to the array
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result.push(q.dequeue());
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// append `0` & `1` respectively
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const s1 = `${result[i]}0`;
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const s2 = `${result[i]}1`;
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// push the combinations in the queue
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q.enqueue(s1);
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q.enqueue(s2);
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}
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// return the result containing all the binary numbers
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return result;
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}
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// console.log(generateBinaryNumber(5));
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module.exports = generateBinaryNumber;
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const Stack = require('../../Stack');
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class Queue {
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constructor() {
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this.queue = new Stack();
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this.temp = new Stack();
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}
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enqueue(data) {
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this.queue.push(data);
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}
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dequeue() {
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if (!this.queue.peek()) {
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return null;
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}
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// pop all the element to the temp stack
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while (this.queue.peek()) this.temp.push(this.queue.pop());
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const el = this.temp.pop();
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// push all the temp items to the queue again
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while (this.temp.peek()) this.queue.push(this.temp.pop());
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return el;
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}
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}
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module.exports = Queue;
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// eslint-disable-next-line no-unused-vars
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const Queue = require('../index');
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const Stack = require('../../Stack');
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function reverseFirstKElelments(q, k) {
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const s = new Stack();
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// push all the k elements ot the stack
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for (let i = 0; i < k; i += 1) {
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s.push(q.dequeue());
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}
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// push the stack items to the queue
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for (let i = 0; i < k; i += 1) {
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q.enqueue(s.pop());
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}
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// empty the queue and push the same queue
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const remaining = q.length() - k;
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for (let i = 0; i < remaining; i += 1) {
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q.enqueue(q.dequeue());
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}
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// return the queue
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return q;
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}
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module.exports = reverseFirstKElelments;
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// let q = new Queue();
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// q.enqueue(1);
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// q.enqueue(2);
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// q.enqueue(3);
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// q.enqueue(4);
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// q.enqueue(5);
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// q.enqueue(6);
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// q.enqueue(7);
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// q.enqueue(8);
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// q.enqueue(9);
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// q = reverseFirstKElelments(q, 4);
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// const arr = [];
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// while (q.length()) {
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// arr.push(q.dequeue());
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// }
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// console.log(arr);

‎src/_DataStructures_/Stack/index.js‎

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