From a3d841e1ffbd319bb9c31d3c5bf9318de23ea7c1 Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 11:44:36 +0530
Subject: [PATCH 1/7] update: added tail of LL

---
 src/_DataStructures_/LinkedList/index.js | 36 +++++++++++++-----------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/src/_DataStructures_/LinkedList/index.js b/src/_DataStructures_/LinkedList/index.js
index 1704c3c4..62a85b3c 100644
--- a/src/_DataStructures_/LinkedList/index.js
+++ b/src/_DataStructures_/LinkedList/index.js
@@ -2,36 +2,42 @@ class Node {
   constructor(data, next) {
     this.data = data;
     this.next = next;
+    this.length = 0;
   }
 }
 
 class LinkedList {
   constructor() {
     this.head = null;
+    this.tail = null;
   }
 
   addAtBeginning(element) {
     this.head = new Node(element, this.head);
+    if (!this.tail) {
+      this.tail = this.head;
+    }
+    return this.head;
   }
 
   addAtEnd(element) {
-    const node = new Node(element, null);
-
     if (!this.head) {
-      this.head = node;
-    } else {
-      let address = this.head;
-      while (address.next) {
-        address = address.next;
-      }
-      address.next = node;
+      return this.addAtBeginning(element);
     }
+    const node = new Node(element, null);
+    this.tail.next = node;
+    this.tail = node;
+    return node;
   }
 
   removeFromBeginning() {
     if (!this.head) {
+      this.tail = null;
       return null;
     }
+    if (this.head.next === null) {
+      this.tail = this.head;
+    }
     const node = this.head;
     this.head = this.head.next;
     return node;
@@ -47,8 +53,10 @@ class LinkedList {
       address = address.next;
     }
 
-    const node = address.next;
-    address.next = null;
+    this.tail = address;
+
+    const node = this.tail.next;
+    this.tail.next = null;
     return node;
   }
 
@@ -63,11 +71,7 @@ class LinkedList {
     if (!this.head) {
       return null;
     }
-    let address = this.head;
-    while (address.next) {
-      address = address.next;
-    }
-    return address;
+    return this.tail;
   }
 
   getAt(index) {

From 63ac6320f1d201e009c32e87e0efd6b94fba93f5 Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 11:52:18 +0530
Subject: [PATCH 2/7] update: size property aded

---
 src/_DataStructures_/LinkedList/index.js | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/_DataStructures_/LinkedList/index.js b/src/_DataStructures_/LinkedList/index.js
index 62a85b3c..fd1ed9c2 100644
--- a/src/_DataStructures_/LinkedList/index.js
+++ b/src/_DataStructures_/LinkedList/index.js
@@ -2,7 +2,6 @@ class Node {
   constructor(data, next) {
     this.data = data;
     this.next = next;
-    this.length = 0;
   }
 }
 
@@ -10,6 +9,7 @@ class LinkedList {
   constructor() {
     this.head = null;
     this.tail = null;
+    this.size = 0;
   }
 
   addAtBeginning(element) {
@@ -17,6 +17,7 @@ class LinkedList {
     if (!this.tail) {
       this.tail = this.head;
     }
+    this.size += 1;
     return this.head;
   }
 
@@ -27,12 +28,12 @@ class LinkedList {
     const node = new Node(element, null);
     this.tail.next = node;
     this.tail = node;
+    this.size += 1;
     return node;
   }
 
   removeFromBeginning() {
     if (!this.head) {
-      this.tail = null;
       return null;
     }
     if (this.head.next === null) {
@@ -40,6 +41,7 @@ class LinkedList {
     }
     const node = this.head;
     this.head = this.head.next;
+    this.size -= 1;
     return node;
   }
 
@@ -57,6 +59,7 @@ class LinkedList {
 
     const node = this.tail.next;
     this.tail.next = null;
+    this.size -= 1;
     return node;
   }
 
@@ -108,8 +111,10 @@ 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) {
@@ -133,21 +138,18 @@ class LinkedList {
 
     const node = address;
     previous.next = address.next.next;
+    this.size -= 1;
     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;
   }
 }
 

From cbe4a1eb7e025c1c4797fbfa61a6bac4ba0c7bf9 Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 13:21:39 +0530
Subject: [PATCH 3/7] update: implemented Queue using SLL

---
 src/_DataStructures_/Queue/QueueUsingArray.js | 20 +++++++
 src/_DataStructures_/Queue/index.js           | 55 ++++++++++++++++---
 2 files changed, 66 insertions(+), 9 deletions(-)
 create mode 100644 src/_DataStructures_/Queue/QueueUsingArray.js

diff --git a/src/_DataStructures_/Queue/QueueUsingArray.js b/src/_DataStructures_/Queue/QueueUsingArray.js
new file mode 100644
index 00000000..99d1861c
--- /dev/null
+++ b/src/_DataStructures_/Queue/QueueUsingArray.js
@@ -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;
diff --git a/src/_DataStructures_/Queue/index.js b/src/_DataStructures_/Queue/index.js
index d51bcab0..641724f1 100644
--- a/src/_DataStructures_/Queue/index.js
+++ b/src/_DataStructures_/Queue/index.js
@@ -1,20 +1,57 @@
-class Queue {
+const { LinkedList: SinglyLinkedLists, Node } = require('../LinkedList');
+
+class Queue extends SinglyLinkedLists {
   constructor() {
-    this.data = [];
+    super();
+    this.NotAllowed = 'Not Allowed';
+  }
+
+  enqueue(data) {
+    const node = new Node(data, null);
+    return this.addAtEnd(node);
   }
 
-  add(element) {
-    // add element to the start of the data
-    return this.data.unshift(element);
+  dequeue() {
+    const node = this.removeFromBeginning();
+    return node.data;
   }
 
   peek() {
-    return this.data[this.data.length - 1];
+    return this.getLast();
+  }
+
+  size() {
+    return this.length();
+  }
+
+  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);
+  }
+
+  getFirst() {
+    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;
\ No newline at end of file
+module.exports = Queue;

From cc29c56d81137123e41ade2ceb49029874323331 Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 13:24:05 +0530
Subject: [PATCH 4/7] fix: peek() should show the front item of queue

---
 src/_DataStructures_/Queue/Queue.test.js | 21 +++++++++++----------
 src/_DataStructures_/Queue/index.js      |  4 ++--
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/src/_DataStructures_/Queue/Queue.test.js b/src/_DataStructures_/Queue/Queue.test.js
index ebe7205c..bca8210f 100644
--- a/src/_DataStructures_/Queue/Queue.test.js
+++ b/src/_DataStructures_/Queue/Queue.test.js
@@ -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 enqueue() 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.size()).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()', () => {
diff --git a/src/_DataStructures_/Queue/index.js b/src/_DataStructures_/Queue/index.js
index 641724f1..01c04de8 100644
--- a/src/_DataStructures_/Queue/index.js
+++ b/src/_DataStructures_/Queue/index.js
@@ -17,7 +17,7 @@ class Queue extends SinglyLinkedLists {
   }
 
   peek() {
-    return this.getLast();
+    return this.getFirst();
   }
 
   size() {
@@ -41,7 +41,7 @@ class Queue extends SinglyLinkedLists {
     throw new Error(this.NotAllowed);
   }
 
-  getFirst() {
+  getLast() {
     throw new Error(this.NotAllowed);
   }
 

From 515f4234bf9435949cf427578561b3956dfd0500 Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 13:40:23 +0530
Subject: [PATCH 5/7] fix: change in Queue APIs

---
 src/_DataStructures_/LinkedList/index.js | 11 +++++++---
 src/_DataStructures_/Queue/Queue.test.js | 26 ++++++++++++------------
 src/_DataStructures_/Queue/index.js      | 19 ++++++++++++-----
 3 files changed, 35 insertions(+), 21 deletions(-)

diff --git a/src/_DataStructures_/LinkedList/index.js b/src/_DataStructures_/LinkedList/index.js
index fd1ed9c2..e7964c01 100644
--- a/src/_DataStructures_/LinkedList/index.js
+++ b/src/_DataStructures_/LinkedList/index.js
@@ -22,13 +22,16 @@ class LinkedList {
   }
 
   addAtEnd(element) {
+    const node = new Node(element, null);
+    this.size += 1;
+
     if (!this.head) {
-      return this.addAtBeginning(element);
+      this.head = node;
+      this.tail = node;
+      return node;
     }
-    const node = new Node(element, null);
     this.tail.next = node;
     this.tail = node;
-    this.size += 1;
     return node;
   }
 
@@ -42,6 +45,7 @@ class LinkedList {
     const node = this.head;
     this.head = this.head.next;
     this.size -= 1;
+    node.next = null;
     return node;
   }
 
@@ -139,6 +143,7 @@ class LinkedList {
     const node = address;
     previous.next = address.next.next;
     this.size -= 1;
+    node.next = null;
     return node;
   }
 
diff --git a/src/_DataStructures_/Queue/Queue.test.js b/src/_DataStructures_/Queue/Queue.test.js
index bca8210f..bdbc6f26 100644
--- a/src/_DataStructures_/Queue/Queue.test.js
+++ b/src/_DataStructures_/Queue/Queue.test.js
@@ -12,9 +12,9 @@ describe('Data Structure : Queue', () => {
       queue = new Queue();
     });
 
-    it('Should enqueue() element to a queue', () => {
+    it('Should add element to a queue', () => {
       queue.enqueue(5);
-      expect(queue.peek()).toEqual([5]);
+      expect(queue.peek()).toEqual(5);
     });
 
     it('Should dequeue() an element from the queue', () => {
@@ -23,7 +23,7 @@ describe('Data Structure : Queue', () => {
 
       expect(queue.dequeue()).toEqual(2);
       expect(queue.peek()).toEqual(3);
-      expect(queue.size()).toEqual(1);
+      expect(queue.length()).toEqual(1);
     });
 
     describe('peek()', () => {
@@ -38,21 +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);
     });
   });
 });
diff --git a/src/_DataStructures_/Queue/index.js b/src/_DataStructures_/Queue/index.js
index 01c04de8..4e097b16 100644
--- a/src/_DataStructures_/Queue/index.js
+++ b/src/_DataStructures_/Queue/index.js
@@ -7,8 +7,7 @@ class Queue extends SinglyLinkedLists {
   }
 
   enqueue(data) {
-    const node = new Node(data, null);
-    return this.addAtEnd(node);
+    return this.addAtEnd(data);
   }
 
   dequeue() {
@@ -17,11 +16,12 @@ class Queue extends SinglyLinkedLists {
   }
 
   peek() {
-    return this.getFirst();
+    const node = this.getFirst();
+    return node.data;
   }
 
-  size() {
-    return this.length();
+  length() {
+    return this.size;
   }
 
   destroy() {
@@ -54,4 +54,13 @@ class Queue extends SinglyLinkedLists {
   }
 }
 
+const q = new Queue();
+
+q.enqueue(10);
+q.enqueue(101);
+q.enqueue(44);
+
+console.log(q.length());
+console.log(q.dequeue());
+
 module.exports = Queue;

From aa9e66fb626e05ce9c6de764e4d7ee557d24a8b0 Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 13:47:37 +0530
Subject: [PATCH 6/7] fix: change in equality, fix in test case for new Queue
 API

---
 src/_DataStructures_/Queue/index.js           |  4 ++--
 src/_DataStructures_/Queue/weave/index.js     |  8 ++++----
 .../Queue/weave/weave.test.js                 | 20 +++++++++----------
 3 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/src/_DataStructures_/Queue/index.js b/src/_DataStructures_/Queue/index.js
index 4e097b16..acbdfb01 100644
--- a/src/_DataStructures_/Queue/index.js
+++ b/src/_DataStructures_/Queue/index.js
@@ -12,12 +12,12 @@ class Queue extends SinglyLinkedLists {
 
   dequeue() {
     const node = this.removeFromBeginning();
-    return node.data;
+    return node ? node.data : node;
   }
 
   peek() {
     const node = this.getFirst();
-    return node.data;
+    return node ? node.data : node;
   }
 
   length() {
diff --git a/src/_DataStructures_/Queue/weave/index.js b/src/_DataStructures_/Queue/weave/index.js
index 94d1d660..5a6da801 100644
--- a/src/_DataStructures_/Queue/weave/index.js
+++ b/src/_DataStructures_/Queue/weave/index.js
@@ -4,12 +4,12 @@ function weaveQueues(first, second) {
   const weaved = new Queue();
 
   while (first.peek() || second.peek()) {
-    if (first.peek() !== undefined) {
-      weaved.add(first.remove());
+    if (first.peek()) {
+      weaved.enqueue(first.dequeue());
     }
 
-    if (second.peek() !== undefined) {
-      weaved.add(second.remove());
+    if (second.peek()) {
+      weaved.enqueue(second.dequeue());
     }
   }
   return weaved;
diff --git a/src/_DataStructures_/Queue/weave/weave.test.js b/src/_DataStructures_/Queue/weave/weave.test.js
index da307f36..05c43ec0 100644
--- a/src/_DataStructures_/Queue/weave/weave.test.js
+++ b/src/_DataStructures_/Queue/weave/weave.test.js
@@ -10,18 +10,18 @@ describe('Weave two queues using weaveQueues()', () => {
     const q1 = new Queue();
     const q2 = new Queue();
 
-    q1.add('Hello');
-    q2.add(1);
-    q1.add('World');
-    q2.add(2);
-    q2.add(3);
+    q1.enqueue('Hello');
+    q2.enqueue(1);
+    q1.enqueue('World');
+    q2.enqueue(2);
+    q2.enqueue(3);
 
     const q3 = weaveQueues(q1, q2);
 
-    expect(q3.remove()).toEqual('Hello');
-    expect(q3.remove()).toEqual(1);
-    expect(q3.remove()).toEqual('World');
-    expect(q3.remove()).toEqual(2);
-    expect(q3.remove()).toEqual(3);
+    expect(q3.dequeue()).toEqual('Hello');
+    expect(q3.dequeue()).toEqual(1);
+    expect(q3.dequeue()).toEqual('World');
+    expect(q3.dequeue()).toEqual(2);
+    expect(q3.dequeue()).toEqual(3);
   });
 });

From d48713ce85cfc2f314371d0181b36239615116df Mon Sep 17 00:00:00 2001
From: Ashok Dey <ashokdey100@gmail.com>
Date: Sun, 13 Oct 2019 13:48:04 +0530
Subject: [PATCH 7/7] cleanup

---
 src/_DataStructures_/Queue/index.js | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/src/_DataStructures_/Queue/index.js b/src/_DataStructures_/Queue/index.js
index acbdfb01..9056c130 100644
--- a/src/_DataStructures_/Queue/index.js
+++ b/src/_DataStructures_/Queue/index.js
@@ -1,4 +1,4 @@
-const { LinkedList: SinglyLinkedLists, Node } = require('../LinkedList');
+const { LinkedList: SinglyLinkedLists } = require('../LinkedList');
 
 class Queue extends SinglyLinkedLists {
   constructor() {
@@ -54,13 +54,4 @@ class Queue extends SinglyLinkedLists {
   }
 }
 
-const q = new Queue();
-
-q.enqueue(10);
-q.enqueue(101);
-q.enqueue(44);
-
-console.log(q.length());
-console.log(q.dequeue());
-
 module.exports = Queue;