new refrences

Author: amejiarosario

lib/data-structures/linked-lists/linked-list-1.js

@@ -0,0 +1,80 @@
+const Node = require('./node');
+
+/**
+ * Singly linked list
+ */
+class LinkedList {
+  constructor() {
+    this.root = null;
+  }
+
+  /**
+   * Adds element to the end of the list (tail)
+   * Runtime: O(n)
+   * @param {any} value
+   */
+  addLast(value) { // similar Array.push
+    const node = new Node(value);
+
+    if(this.root) {
+      let currentNode = this.root;
+      while(currentNode && currentNode.next) {
+        currentNode = currentNode.next;
+      }
+      currentNode.next = node;
+    } else {
+      this.root = node;
+    }
+  }
+
+  /**
+   * Removes element from the start of the list (head/root)
+   * Runtime: O(1)
+   */
+  removeFirst() { // similar Array.shift
+    const first = this.root;
+
+    if(first) {
+      this.root = first.next;
+      return first.value;
+    }
+  }
+
+  /**
+   * Adds element to the begining of the list
+   * Runtime: O(1)
+   * @param {any} value
+   */
+  addFirst(value) { // similar to Array.unshift
+    const node = new Node(value);
+    node.next = this.root;
+    this.root = node;
+  }
+
+  /**
+   * Removes element to the end of the list
+   * similar to Array.pop
+   * Runtime: O(n)
+   */
+  removeLast() {
+    let current = this.root;
+    let target;
+
+    if(current && current.next) {
+      while(current && current.next && current.next.next) {
+        current = current.next;
+      }
+      target = current.next;
+      current.next = null;
+    } else {
+      this.root = null;
+      target = current;
+    }
+
+    if(target) {
+      return target.value;
+    }
+  }
+}
+
+module.exports = LinkedList;

lib/data-structures/linked-lists/linked-list.js

@@ -5,50 +5,50 @@ const Node = require('./node');
  */
 class LinkedList {
   constructor() {
-    this.root = null;
+    this.first = null; // head/root element
   }
 
   /**
-   * Adds element to the end of the list (tail)
+   * Adds element to the end of the list (tail). Similar to Array.push
    * Runtime: O(n)
    * @param {any} value
    */
-  addLast(value) { // similar Array.push
+  addLast(value) {
     const node = new Node(value);
 
-    if(this.root) {
-      let currentNode = this.root;
+    if(this.first) {
+      let currentNode = this.first;
       while(currentNode && currentNode.next) {
         currentNode = currentNode.next;
       }
       currentNode.next = node;
     } else {
-      this.root = node;
+      this.first = node;
     }
   }
 
   /**
-   * Removes element from the start of the list (head/root)
+   * Removes element from the start of the list (head/root). similar Array.shift
    * Runtime: O(1)
    */
-  removeFirst() { // similar Array.shift
-    const first = this.root;
+  removeFirst() {
+    const first = this.first;
 
     if(first) {
-      this.root = first.next;
+      this.first = first.next;
       return first.value;
     }
   }
 
   /**
-   * Adds element to the begining of the list
+   * Adds element to the begining of the list. Similar to Array.unshift
    * Runtime: O(1)
    * @param {any} value
    */
-  addFirst(value) { // similar to Array.unshift
+  addFirst(value) {
     const node = new Node(value);
-    node.next = this.root;
-    this.root = node;
+    node.next = this.first;
+    this.first = node;
   }
 
   /**
@@ -57,7 +57,7 @@ class LinkedList {
    * Runtime: O(n)
    */
   removeLast() {
-    let current = this.root;
+    let current = this.first;
     let target;
 
     if(current && current.next) {
@@ -67,7 +67,7 @@ class LinkedList {
       target = current.next;
       current.next = null;
     } else {
-      this.root = null;
+      this.first = null;
       target = current;
     }
 

lib/data-structures/linked-lists/linked-list.spec.js

@@ -10,17 +10,17 @@ describe('LinkedList', function () {
   describe('#addLast', () => {
     it('should add element to end/tail of the list', () => {
       linkedList.addLast('a');
-      expect(linkedList.root.value).toBe('a');
+      expect(linkedList.first.value).toBe('a');
     });
 
     it('should link values', () => {
       linkedList.addLast('a');
       linkedList.addLast('b');
       linkedList.addLast('c');
 
-      expect(linkedList.root.value).toBe('a');
-      expect(linkedList.root.next.value).toBe('b');
-      expect(linkedList.root.next.next.value).toBe('c');
+      expect(linkedList.first.value).toBe('a');
+      expect(linkedList.first.next.value).toBe('b');
+      expect(linkedList.first.next.next.value).toBe('c');
     });
   });
 
@@ -32,8 +32,8 @@ describe('LinkedList', function () {
 
     it('should remove first item: a', () => {
       expect(linkedList.removeFirst()).toBe('a');
-      expect(linkedList.root.value).toBe('b');
-      expect(linkedList.root.next).toBe(null);
+      expect(linkedList.first.value).toBe('b');
+      expect(linkedList.first.next).toBe(null);
 
       expect(linkedList.removeFirst()).toBe('b');
       expect(linkedList.removeFirst()).toBe(undefined);
@@ -44,14 +44,14 @@ describe('LinkedList', function () {
   describe('#addFirst', () => {
     it('add element to the head/root of the list', () => {
       linkedList.addFirst('a');
-      expect(linkedList.root.value).toBe('a');
+      expect(linkedList.first.value).toBe('a');
     });
 
     it('add element to the head/root of the list', () => {
       linkedList.addFirst('a');
       linkedList.addFirst('b');
-      expect(linkedList.root.value).toBe('b');
-      expect(linkedList.root.next.value).toBe('a');
+      expect(linkedList.first.value).toBe('b');
+      expect(linkedList.first.next.value).toBe('a');
     });
   });
 
@@ -65,8 +65,8 @@ describe('LinkedList', function () {
     it('should remove first item', () => {
       expect(linkedList.removeLast()).toBe('c');
       expect(linkedList.removeLast()).toBe('b');
-      expect(linkedList.root.value).toBe('a');
-      expect(linkedList.root.next).toBe(null);
+      expect(linkedList.first.value).toBe('a');
+      expect(linkedList.first.next).toBe(null);
 
       expect(linkedList.removeLast()).toBe('a');
       expect(linkedList.removeLast()).toBe(undefined);

lib/data-structures/linked-lists/node-1.js

@@ -0,0 +1,11 @@
+/**
+ * Simple node
+ */
+class Node {
+  constructor(value) {
+    this.value = value;
+    this.next = null;
+  }
+}
+
+module.exports = Node;

lib/data-structures/linked-lists/node.js

@@ -1,10 +1,11 @@
 /**
- * Simple node
+ * Node with reference to next and previous element
  */
 class Node {
   constructor(value) {
     this.value = value;
     this.next = null;
+    this.previous = null;
   }
 }