chore: rever the linked list

Author: rupeshtiwari

README.md

@@ -161,6 +161,15 @@ The newly created node will become head of the linked list. · Size of the list
 We’re given the pointer/reference to the head of a singly linked list, reverse it and return the pointer/reference to the head of the reversed linked list.
 
 ![](https://i.imgur.com/lamsYrL.png)
+
+Problem Solving steps
+
+![](https://i.imgur.com/0wZ4lB1.png)
+
+Running program output
+
+![](https://i.imgur.com/FAHJMeF.png)
+
 ### Stack
 
 Depth First Search (DFS) uses a `stack` for storing the nodes that it is visiting.

src/2-linked-list/2-reverse-singly-linked-list.mjs

@@ -0,0 +1,99 @@
+import { creatLinkedListFromArray } from './1-implement-linked-list.mjs';
+import { display } from './1-implement-linked-list.mjs';
+
+/**
+ * 2->3->4->5->6->null
+ * R  L
+ *
+ * 2->null
+ *
+ * 3->2->null
+ * R
+ * 4->5->6->null
+ * L
+ *
+ * 4->3->2->null
+ * R
+ * 5->6->null
+ * L
+ *
+ * 5->4->3->2->null
+ * R
+ * 6->null
+ * L
+ *
+ * 6->5->4->3->2->null
+ * R
+ *
+ */
+
+/**
+ *  2->3->4->5->6
+ * 
+ *  R->2;
+ *  L ->3; 
+ *   
+ *  R.next = null
+ *  l points next 
+ *      temp = L.next
+        L.next = R
+        R = L
+        L = temp
+
+ *  L.next = R
+    R = L            
+ */
+
+/**
+ * runtime complexity: O(n) because reverse the list in single loop
+ * space/memory complexity: O(1) because it is iterative
+ * @param head head
+ * @returns reversed head
+ */
+function reverse(head) {
+  let reverse = head;
+  let listToDo = head.next;
+
+  head.next = null;
+
+  while (listToDo) {
+    let temp = listToDo.next;
+    listToDo.next = reverse;
+    reverse = listToDo;
+    listToDo = temp;
+  }
+
+  return reverse;
+}
+
+const head = creatLinkedListFromArray([2, 3, 4, 5, 6]);
+const reversedHead = reverse(head);
+console.log(display(reversedHead));
+
+/** TEST
+ * 2-3-4-5-6
+ * R L
+ *
+ * 2-null
+ *
+ * 3-2-null
+ * R
+ * 4-5-6-null
+ * L
+ *
+ * 4-3-2-null
+ * R
+ * 5-6-null
+ * L
+ *
+ * 5-4-3-2-null
+ * R
+ * 6-null
+ * L
+ *
+ * 6-5-4-3-2-null
+ * R
+ *
+ * null
+ * L
+ */