Added Explanation to reversing a linked list

Author: Sagar

Linked List/reverse_linked_list.java

@@ -8,6 +8,31 @@
  *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  * }
  */
+
+/*Explaination of the code which reverses the linked list
+* --> Initially we are given the head of the linked list. The approach used here is that
+* for reversing the linked list we can take the user of three pointers
+*
+* --> These pointers are named as prev, curr, and right. Initially prev points to NULL, curr
+* points to the current node (node of which the pointer has to be reversed) and the right node
+* which always points to the node next to the current
+*
+* --> Idea here is that at each pass we will be reversing the pointer of the current node and
+* move all the pointers forward by one step
+*
+* --> So initially, the current node points to head node, it's pointer is reversed and is made to
+* point to he NULL, since now this first node becomes the last node.
+*
+* --> To move forward, prev is now at the location of current node, current node moves by
+* one step, by making it point to the location where right is pointing now. (Using right pointer
+* since the track of the next node is lost as we have reveresed the pointer).
+*
+* --> Loop stops when the current node becomes null. At the itereation, last node is being pointed
+* by prev, which is now the first node logically, so assign head to prev.
+*
+* --> Example input: 1->2->3->4->5
+*     Output : 5->4->3->2->1
+* */
 class Solution {
     public ListNode reverseList(ListNode head) {
         ListNode prev=null;