Add 'size()' method in linked list data structure and also written te…

[bhaveshmhadse]

Update file src/data-structures/linked-list/LinkedList.js and src/data-structures/linked-list/test/LinkedList.test.js

• src/data-structures/linked-list/LinkedList.js

Before

After

   /**
   * @returns {Number}
   */
  size() {
    // If head is null the size of linked list will be -1 or 0, So here we return -1.
    if (!this.head) {
      return -1;
    }

    let size = 0;
    let currentNode = this.head;

    // Traverse to the linked list and update the size.
    while (currentNode) {
      size += 1;
      currentNode = currentNode.next;
    }

    return size;
  }

• src/data-structures/linked-list/test/LinkedList.test.js

Before

After

  it('should return the size of linked list', () => {
    const linkedList = new LinkedList();

    linkedList.append(1);
    linkedList.append(2);
    linkedList.append(3);

    expect(linkedList.size()).toBe(3);
  });