Add 'size()' method in linked list data structure and also written test case for it.

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

@@ -269,4 +269,25 @@ export default class LinkedList {
 
     return this;
   }
+
+  /**
+   * @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

@@ -157,9 +157,7 @@ describe('LinkedList', () => {
     const nodeValue1 = { value: 1, key: 'key1' };
     const nodeValue2 = { value: 2, key: 'key2' };
 
-    linkedList
-      .append(nodeValue1)
-      .prepend(nodeValue2);
+    linkedList.append(nodeValue1).prepend(nodeValue2);
 
     const nodeStringifier = (value) => `${value.key}:${value.value}`;
 
@@ -174,9 +172,7 @@ describe('LinkedList', () => {
     linkedList.append(1);
     expect(linkedList.find({ value: 1 })).toBeDefined();
 
-    linkedList
-      .append(2)
-      .append(3);
+    linkedList.append(2).append(3);
 
     const node = linkedList.find({ value: 2 });
 
@@ -192,7 +188,9 @@ describe('LinkedList', () => {
       .append({ value: 2, key: 'test2' })
       .append({ value: 3, key: 'test3' });
 
-    const node = linkedList.find({ callback: (value) => value.key === 'test2' });
+    const node = linkedList.find({
+      callback: (value) => value.key === 'test2',
+    });
 
     expect(node).toBeDefined();
     expect(node.value.value).toBe(2);
@@ -258,10 +256,7 @@ describe('LinkedList', () => {
     const linkedList = new LinkedList();
 
     // Add test values to linked list.
-    linkedList
-      .append(1)
-      .append(2)
-      .append(3);
+    linkedList.append(1).append(2).append(3);
 
     expect(linkedList.toString()).toBe('1,2,3');
     expect(linkedList.head.value).toBe(1);
@@ -279,4 +274,14 @@ describe('LinkedList', () => {
     expect(linkedList.head.value).toBe(1);
     expect(linkedList.tail.value).toBe(3);
   });
+
+  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);
+  });
 });