chore: created singly linked list

Author: rupeshtiwari

README.md

@@ -140,13 +140,21 @@ class LinkedListNode {
 
 Below are the types of LinkedList:
 
-**Singly Linked List**
+- **Singly Linked List**
+- **Doubly Linked List**
+- **Circular Linked List**
 
-![](https://i.imgur.com/byjRY7x.png)
+  ![](https://i.imgur.com/byjRY7x.png)
 
-**Doubly Linked List**
+#### Insert at head
 
-**Circular Linked List**
+The newly created node will become head of the linked list. · Size of the list is increased by one.
+
+![](https://i.imgur.com/79qwSqL.png)
+
+#### Insert at tail
+
+![](https://i.imgur.com/Wz9Uovq.png)
 
 ### Stack
 

src/2-linked-list/1-implement-linked-list.mjs

@@ -6,5 +6,77 @@ class LinkedListNode {
 }
 
 class LinkedList {
-    
-}
+  constructor() {
+    this.head = null;
+    this.length = 0;
+  }
+
+  insertAtHead(value) {
+    var newNode = new LinkedListNode(value);
+    newNode.next = this.head;
+    this.head = newNode;
+    this.length++;
+
+    return newNode;
+  }
+
+  insertAtTail(value) {
+    var newNode = new LinkedListNode(value);
+    let head = this.head;
+
+    if (!head) {
+      head = newNode;
+      this.length++;
+
+      return newNode;
+    }
+
+    let temp = head;
+
+    while (temp.next) {
+      temp = temp.next;
+    }
+
+    // temp is tail
+    temp.next = newNode;
+
+    this.length++;
+
+    return newNode;
+  }
+
+  toString() {
+    if (!this.head) {
+      return '';
+    }
+
+    let temp = this.head;
+    let data = '';
+
+    while (temp) {
+      data += ',' + temp.data;
+      temp = temp.next;
+    }
+
+    return data.substr(1,data.length);
+  }
+}
+
+function createRandomLinkedList(length) {
+  const list = new LinkedList();
+  for (let i = 0; i < length; i++) {
+    list.insertAtHead(Math.floor(Math.random() * 100 + 1));
+  }
+
+  return list;
+}
+
+// Test-----------------------
+const list = new LinkedList();
+list.insertAtHead(2);
+console.log(list.toString());
+
+list.insertAtTail(5);
+console.log(list.toString());
+
+console.log(createRandomLinkedList(20).toString());