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Problems involving Queues #81

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TheSTL merged 13 commits into master from problems
Oct 13, 2019
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4 changes: 3 additions & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -30,10 +30,12 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
- [Remove Consecutive Repeated Digits](src/_DataStructures_/Stack/remove-consecutive-repeated-digits)
- [Implement 2 Stacks using Single Array](src/_DataStructures_/Stack/2-stacks-using1-array)


- [Queue](src/_DataStructures_/Queue)

- [Weave](src/_DataStructures_/Queue/weave)
- [Reverse First K Elements of a Queue](src/_DataStructures_/Queue/reverse-first-k)
- [Generate all Binary Numbers from 1 to N](src/_DataStructures_/Queue/generate-binary-number)
- [Queue using Stack](src/_DataStructures_/Queue/queue-using-stack)

- [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)

Expand Down
55 changes: 33 additions & 22 deletions src/_DataStructures_/LinkedList/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -8,32 +8,44 @@ class Node {
class LinkedList {
constructor() {
this.head = null;
this.tail = null;
this.size = 0;
}

addAtBeginning(element) {
this.head = new Node(element, this.head);
if (!this.tail) {
this.tail = this.head;
}
this.size += 1;
return this.head;
}

addAtEnd(element) {
const node = new Node(element, null);
this.size += 1;

if (!this.head) {
this.head = node;
} else {
let address = this.head;
while (address.next) {
address = address.next;
}
address.next = node;
this.tail = node;
return node;
}
this.tail.next = node;
this.tail = node;
return node;
}

removeFromBeginning() {
if (!this.head) {
return null;
}
if (this.head.next === null) {
this.tail = this.head;
}
const node = this.head;
this.head = this.head.next;
this.size -= 1;
node.next = null;
return node;
}

Expand All @@ -47,8 +59,11 @@ class LinkedList {
address = address.next;
}

const node = address.next;
address.next = null;
this.tail = address;

const node = this.tail.next;
this.tail.next = null;
this.size -= 1;
return node;
}

Expand All @@ -63,11 +78,7 @@ class LinkedList {
if (!this.head) {
return null;
}
let address = this.head;
while (address.next) {
address = address.next;
}
return address;
return this.tail;
}

getAt(index) {
Expand Down Expand Up @@ -104,8 +115,10 @@ class LinkedList {
count -= 1;
}

previous.next = new Node(element, previous.next);
return null;
const node = new Node(element, previous.next);
previous.next = node;
this.size += 1;
return node;
}

removeAt(index) {
Expand All @@ -129,21 +142,19 @@ class LinkedList {

const node = address;
previous.next = address.next.next;
this.size -= 1;
node.next = null;
return node;
}

length() {
let address = this.head;
let count = 0;
while (address) {
count += 1;
address = address.next;
}
return count;
return this.size;
}

delete() {
this.head = null;
this.tail = this.head;
this.size = 0;
}
}

Expand Down
41 changes: 21 additions & 20 deletions src/_DataStructures_/Queue/Queue.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -12,23 +12,24 @@ describe('Data Structure : Queue', () => {
queue = new Queue();
});

it('Should add() element to a queue', () => {
queue.add(5);
expect(queue.data).toEqual([5]);
it('Should add element to a queue', () => {
queue.enqueue(5);
expect(queue.peek()).toEqual(5);
});

it('Should remove() an element from the queue', () => {
queue.add(2);
queue.add(3);
it('Should dequeue() an element from the queue', () => {
queue.enqueue(2);
queue.enqueue(3);

expect(queue.remove()).toEqual(2);
expect(queue.data).toEqual([3]);
expect(queue.dequeue()).toEqual(2);
expect(queue.peek()).toEqual(3);
expect(queue.length()).toEqual(1);
});

describe('peek()', () => {
beforeEach(() => {
queue.add(2);
queue.add(5);
queue.enqueue(2);
queue.enqueue(5);
});

it('Should return the elemet to be removed using peek()', () => {
Expand All @@ -37,21 +38,21 @@ describe('Data Structure : Queue', () => {

it('Should not remove the element', () => {
expect(queue.peek()).toEqual(2);
expect(queue.remove()).toEqual(2);
expect(queue.dequeue()).toEqual(2);
});
});

it('Should maintain the order of elements', () => {
// first in first out
queue.add(2);
queue.add(1);
queue.add(4);
queue.add(3);

expect(queue.remove()).toEqual(2);
expect(queue.remove()).toEqual(1);
expect(queue.remove()).toEqual(4);
expect(queue.remove()).toEqual(3);
queue.enqueue(2);
queue.enqueue(1);
queue.enqueue(4);
queue.enqueue(3);

expect(queue.dequeue()).toEqual(2);
expect(queue.dequeue()).toEqual(1);
expect(queue.dequeue()).toEqual(4);
expect(queue.dequeue()).toEqual(3);
});
});
});
20 changes: 20 additions & 0 deletions src/_DataStructures_/Queue/QueueUsingArray.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
class Queue {
constructor() {
this.data = [];
}

add(element) {
// add element to the start of the data
return this.data.unshift(element);
}

peek() {
return this.data[this.data.length - 1];
}

remove() {
return this.data.pop();
}
}

module.exports = Queue;
29 changes: 29 additions & 0 deletions src/_DataStructures_/Queue/generate-binary-number/index.js
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@@ -0,0 +1,29 @@
const Queue = require('../index');

function generateBinaryNumber(n) {
const result = [];
const q = new Queue();

// add `1` to the queue
q.enqueue('1');

// iterate till the given number
for (let i = 0; i < n; i += 1) {
// push the item in the queue to the array
result.push(q.dequeue());

// append `0` & `1` respectively
const s1 = `${result[i]}0`;
const s2 = `${result[i]}1`;

// push the combinations in the queue
q.enqueue(s1);
q.enqueue(s2);
}
// return the result containing all the binary numbers
return result;
}

// console.log(generateBinaryNumber(5));

module.exports = generateBinaryNumber;
55 changes: 46 additions & 9 deletions src/_DataStructures_/Queue/index.js
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Original file line number Diff line number Diff line change
@@ -1,20 +1,57 @@
class Queue {
const { LinkedList: SinglyLinkedLists } = require('../LinkedList');

class Queue extends SinglyLinkedLists {
constructor() {
this.data = [];
super();
this.NotAllowed = 'Not Allowed';
}

enqueue(data) {
return this.addAtEnd(data);
}

add(element) {
// add element to the start of the data
return this.data.unshift(element);
dequeue() {
const node = this.removeFromBeginning();
return node ? node.data : node;
}

peek() {
return this.data[this.data.length - 1];
const node = this.getFirst();
return node ? node.data : node;
}

length() {
return this.size;
}

destroy() {
this.delete();
}

/** Override and throw error for other LL methods */
addAtBeginning() {
throw new Error(this.NotAllowed);
}

addAt() {
throw new Error(this.NotAllowed);
}

removeFromEnd() {
throw new Error(this.NotAllowed);
}

getLast() {
throw new Error(this.NotAllowed);
}

getAt() {
throw new Error(this.NotAllowed);
}

remove() {
return this.data.pop();
removeAt() {
throw new Error(this.NotAllowed);
}
}

module.exports = Queue;
module.exports = Queue;
28 changes: 28 additions & 0 deletions src/_DataStructures_/Queue/queue-using-stack/index.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
const Stack = require('../../Stack');

class Queue {
constructor() {
this.queue = new Stack();
this.temp = new Stack();
}

enqueue(data) {
this.queue.push(data);
}

dequeue() {
if (!this.queue.peek()) {
return null;
}

// pop all the element to the temp stack
while (this.queue.peek()) this.temp.push(this.queue.pop());
const el = this.temp.pop();

// push all the temp items to the queue again
while (this.temp.peek()) this.queue.push(this.temp.pop());
return el;
}
}

module.exports = Queue;
48 changes: 48 additions & 0 deletions src/_DataStructures_/Queue/reverse-first-k/index.js
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Original file line number Diff line number Diff line change
@@ -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);
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