Merge pull request #20 from ziadeleraky/LinkedList

Added an intermediate problem with solution (Doubly LinkedList)

Author: devvsakib

L-I/0004 Doubly LinkedList ( L-I )/LinkedList.js

@@ -0,0 +1,147 @@
+class Node {
+  constructor(value) {
+    this.value = value;
+    this.next = null;
+    this.prev = null;
+  }
+}
+
+class LinkedList {
+  constructor(value) {
+    // create a new node with the value passed to the constructor
+    this.head = new Node(value);
+    // set the tail to be the same as the head since there is only one node in the linkedlist
+    this.tail = this.head;
+    this.length = 1;
+  }
+
+  // append a node to the end of the linkedlist
+  append(value) {
+    const node = new Node(value);
+    // set the next property of the tail to be the new node
+    this.tail.next = node;
+    // set the previous property of the new node to be the tail
+    node.prev = this.tail;
+    // set the tail to be the new node
+    this.tail = node;
+    this.length++;
+    return this.print();
+  }
+
+  // prepend a node to the beginning of the linkedlist
+  prepend(value) {
+    const node = new Node(value);
+    // set the next property of the new node to be the head
+    node.next = this.head;
+    // set the previous property of the head to be the new node
+    this.head.prev = node;
+    // set the head to be the new node
+    this.head = node;
+    this.length++;
+    return this.print();
+  }
+
+  // insert a node at a specific index
+  insert(index, value) {
+    const node = new Node(value);
+    // if index is greater than the length of the linkedlist, append the value to the end
+    if (index >= this.length) {
+      this.append(value);
+      return this.print();
+    }
+
+    // if index is 0, prepend the value to the beginning
+    if (index === 0) {
+      this.prepend(value);
+      return this.print();
+    }
+
+    // if index is in the middle of the linkedlist
+    // [1,3,2,5] -- insert(2,55)
+    // leadPointer -> 3
+    let leadPointer = this.traverseToIndex(index - 1);
+    // trailPointer -> 2
+    let trailPointer = leadPointer.next;
+    // set the next of the leadPointer to the new node
+    leadPointer.next = node;
+    // set the previous of the new node to the leadPointer
+    node.prev = leadPointer;
+    // set the next of the new node to the trailPointer
+    node.next = trailPointer;
+    // set the previous of the trailPointer to the new node
+    trailPointer.prev = node;
+    this.length++;
+    return this.print();
+  }
+
+  // remove a node at a specific index
+  remove(index) {
+    // if index is 0, set the head to be the next node
+    if (index === 0) {
+      this.head = this.head.next;
+      this.head.prev = null;
+      this.length--;
+      return this.print();
+    }
+
+    // if index is the last node, set the tail to be the previous node
+    if (index >= this.length) {
+      this.tail = this.tail.prev;
+      this.tail.next = null;
+      this.length--;
+      return this.print();
+    }
+
+    // if index is in the middle of the linkedlist
+    // [1,3,2,5] -- remove(2)
+    // leadPointer -> 3
+    let leadPointer = this.traverseToIndex(index - 1);
+    // trailPointer -> 5
+    let trailPointer = leadPointer.next.next;
+    // set the next of the leadPointer to the trailPointer
+    leadPointer.next = trailPointer;
+    // set the previous of the trailPointer to the leadPointer
+    trailPointer.prev = leadPointer;
+    this.length--;
+    return this.print();
+  }
+
+  traverseToIndex(index) {
+    let counter = 0;
+    let currentNode = this.head;
+    while (counter !== index) {
+      currentNode = currentNode.next;
+      counter++;
+    }
+    return currentNode;
+  }
+
+  // print the linkedlist as an array
+  print() {
+    const array = [];
+    // Start with first item in the linkedlist
+    let currentNode = this.head;
+    while (currentNode !== null) {
+      array.push(currentNode.value);
+      currentNode = currentNode.next;
+    }
+    return array;
+  }
+}
+
+// Test cases
+const myLinkedList = new LinkedList(10);
+myLinkedList.append(5);
+myLinkedList.append(16);
+myLinkedList.prepend(3);
+myLinkedList.insert(2, 55);
+myLinkedList.insert(3, 45);
+myLinkedList.append(22);
+myLinkedList.prepend(1);
+myLinkedList.insert(0, 0);
+myLinkedList.insert(50, 99);
+myLinkedList.remove(0);
+myLinkedList.remove(50);
+myLinkedList.remove(3);
+myLinkedList.remove(3);
+console.log(myLinkedList.print());

L-I/0004 Doubly LinkedList ( L-I )/README.md

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+# 0004 Doubly LinkedList ( L-I )
+
+## Problem
+
+Create a LinkedList that has 4 methods
+
+- Append a node to the end of the linkedlist
+- Prepend a node to the beginning of the linkedlist
+- Insert a node at a specific index
+- Remove a node at a specific index
+
+## References
+
+- [Doubly LinkedList - Medium](https://medium.com/geekculture/doubly-linked-lists-javascript-b13cc21ca59d)
+
+## Problem Added & Solved By
+
+- [Ziad Eleraky](https://github.com/ziadeleraky)