Move linked list traversals into separate section.

src/algorithms/linked-list/reverse-traversal/README.md

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+# Reversed Linked List Traversal
+
+The task is to traverse the given linked list in reversed order.
+
+For example for the following linked list: 
+
+![](https://upload.wikimedia.org/wikipedia/commons/6/6d/Singly-linked-list.svg)
+
+The order of traversal should be:
+
+```text
+37 → 99 → 12
+```
+
+The time complexity is `O(n)` because we visit every node only once.
+
+## Reference
+
+- [Wikipedia](https://en.wikipedia.org/wiki/Linked_list)

src/algorithms/linked-list/reverse-traversal/__test__/reverseTraversal.test.js

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+import LinkedList from '../../../../data-structures/linked-list/LinkedList';
+import reverseTraversal from '../reverseTraversal';
+
+describe('reverseTraversal', () => {
+  it('should traverse linked list in reverse order', () => {
+    const linkedList = new LinkedList();
+
+    linkedList
+      .append(1)
+      .append(2)
+      .append(3);
+
+    const traversedNodeValues = [];
+    const traversalCallback = (nodeValue) => {
+      traversedNodeValues.push(nodeValue);
+    };
+
+    reverseTraversal(linkedList, traversalCallback);
+
+    expect(traversedNodeValues).toEqual([3, 2, 1]);
+  });
+});
+
+
+// it('should reverse traversal the linked list with callback', () => {
+//   const linkedList = new LinkedList();
+//
+//   linkedList
+//     .append(1)
+//     .append(2)
+//     .append(3);
+//
+//   expect(linkedList.toString()).toBe('1,2,3');
+//   expect(linkedList.reverseTraversal(linkedList.head, value => value * 2)).toEqual([6, 4, 2]);
+//   expect(() => linkedList.reverseTraversal(linkedList.head)).toThrow();
+// });

src/algorithms/linked-list/reverse-traversal/reverseTraversal.js

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+/**
+ * Traversal callback function.
+ * @callback traversalCallback
+ * @param {*} nodeValue
+ */
+
+/**
+ * @param {LinkedListNode} node
+ * @param {traversalCallback} callback
+ */
+function reverseTraversalRecursive(node, callback) {
+  if (node) {
+    reverseTraversalRecursive(node.next, callback);
+    callback(node.value);
+  }
+}
+
+/**
+ * @param {LinkedList} linkedList
+ * @param {traversalCallback} callback
+ */
+export default function reverseTraversal(linkedList, callback) {
+  reverseTraversalRecursive(linkedList.head, callback);
+}

src/algorithms/linked-list/traversal/README.md

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+# Linked List Traversal
+
+The task is to traverse the given linked list in straight order.
+
+For example for the following linked list: 
+
+![](https://upload.wikimedia.org/wikipedia/commons/6/6d/Singly-linked-list.svg)
+
+The order of traversal should be:
+
+```text
+12 → 99 → 37
+```
+
+The time complexity is `O(n)` because we visit every node only once.
+
+## Reference
+
+- [Wikipedia](https://en.wikipedia.org/wiki/Linked_list)

src/algorithms/linked-list/traversal/__test__/traversal.test.js

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+import LinkedList from '../../../../data-structures/linked-list/LinkedList';
+import traversal from '../traversal';
+
+describe('traversal', () => {
+  it('should traverse linked list', () => {
+    const linkedList = new LinkedList();
+
+    linkedList
+      .append(1)
+      .append(2)
+      .append(3);
+
+    const traversedNodeValues = [];
+    const traversalCallback = (nodeValue) => {
+      traversedNodeValues.push(nodeValue);
+    };
+
+    traversal(linkedList, traversalCallback);
+
+    expect(traversedNodeValues).toEqual([1, 2, 3]);
+  });
+});

src/algorithms/linked-list/traversal/traversal.js

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+/**
+ * Traversal callback function.
+ * @callback traversalCallback
+ * @param {*} nodeValue
+ */
+
+/**
+ * @param {LinkedList} linkedList
+ * @param {traversalCallback} callback
+ */
+export default function traversal(linkedList, callback) {
+  let currentNode = linkedList.head;
+
+  while (currentNode) {
+    callback(currentNode.value);
+    currentNode = currentNode.next;
+  }
+}