diff --git a/data/progress.txt b/data/progress.txt
index 17e35128..cf075405 100644
--- a/data/progress.txt
+++ b/data/progress.txt
@@ -1,4 +1,4 @@
-20240308: 152,153(again),190,191,198,200
+20240308: 152,153(again),190,191,198,200,206(again)
 20240307: 139(again),141,143(again)
 20240306: 121,124(again),125,128,133(again)
 20240305: 100,102,104,105(again)
diff --git a/data/to_review.txt b/data/to_review.txt
index f50b87e8..2ecbb95f 100644
--- a/data/to_review.txt
+++ b/data/to_review.txt
@@ -1,4 +1,4 @@
-2024-05-02 -> ['152,153(again),190,191,198,200']
+2024-05-02 -> ['152,153(again),190,191,198,200,206(again)']
 2024-05-01 -> ['139(again),141,143(again)']
 2024-04-30 -> ['121,124(again),125,128,133(again)']
 2024-04-29 -> ['100,102,104,105(again)']
@@ -7,7 +7,7 @@
 2024-04-24 -> ['39,48(again),49,53,54']
 2024-04-23 -> ['20,21,23,33(again)']
 2024-04-22 -> ['1,3,5,4,19']
-2024-04-11 -> ['152,153(again),190,191,198,200']
+2024-04-11 -> ['152,153(again),190,191,198,200,206(again)']
 2024-04-10 -> ['139(again),141,143(again)']
 2024-04-09 -> ['121,124(again),125,128,133(again)']
 2024-04-08 -> ['100,102,104,105(again)']
@@ -16,25 +16,25 @@
 2024-04-03 -> ['39,48(again),49,53,54']
 2024-04-02 -> ['20,21,23,33(again)']
 2024-04-01 -> ['1,3,5,4,19']
-2024-03-29 -> ['152,153(again),190,191,198,200']
+2024-03-29 -> ['152,153(again),190,191,198,200,206(again)']
 2024-03-28 -> ['139(again),141,143(again)']
 2024-03-27 -> ['121,124(again),125,128,133(again)']
 2024-03-26 -> ['100,102,104,105(again)']
 2024-03-25 -> ['73,76,79(again),91,25']
 2024-03-24 -> ['55(again),56,62,70']
-2024-03-21 -> ['152,153(again),190,191,198,200', '39,48(again),49,53,54']
+2024-03-21 -> ['152,153(again),190,191,198,200,206(again)', '39,48(again),49,53,54']
 2024-03-20 -> ['139(again),141,143(again)', '20,21,23,33(again)']
 2024-03-19 -> ['121,124(again),125,128,133(again)', '1,3,5,4,19']
 2024-03-18 -> ['100,102,104,105(again)']
 2024-03-17 -> ['73,76,79(again),91,25']
-2024-03-16 -> ['152,153(again),190,191,198,200', '55(again),56,62,70']
+2024-03-16 -> ['152,153(again),190,191,198,200,206(again)', '55(again),56,62,70']
 2024-03-15 -> ['139(again),141,143(again)']
 2024-03-14 -> ['121,124(again),125,128,133(again)']
-2024-03-13 -> ['152,153(again),190,191,198,200', '100,102,104,105(again)', '39,48(again),49,53,54']
+2024-03-13 -> ['152,153(again),190,191,198,200,206(again)', '100,102,104,105(again)', '39,48(again),49,53,54']
 2024-03-12 -> ['139(again),141,143(again)', '73,76,79(again),91,25', '20,21,23,33(again)']
-2024-03-11 -> ['152,153(again),190,191,198,200', '121,124(again),125,128,133(again)', '55(again),56,62,70', '1,3,5,4,19']
-2024-03-10 -> ['152,153(again),190,191,198,200', '139(again),141,143(again)', '100,102,104,105(again)']
-2024-03-09 -> ['152,153(again),190,191,198,200', '139(again),141,143(again)', '121,124(again),125,128,133(again)', '73,76,79(again),91,25']
+2024-03-11 -> ['152,153(again),190,191,198,200,206(again)', '121,124(again),125,128,133(again)', '55(again),56,62,70', '1,3,5,4,19']
+2024-03-10 -> ['152,153(again),190,191,198,200,206(again)', '139(again),141,143(again)', '100,102,104,105(again)']
+2024-03-09 -> ['152,153(again),190,191,198,200,206(again)', '139(again),141,143(again)', '121,124(again),125,128,133(again)', '73,76,79(again),91,25']
 2024-03-08 -> ['139(again),141,143(again)', '121,124(again),125,128,133(again)', '100,102,104,105(again)', '55(again),56,62,70', '39,48(again),49,53,54']
 2024-03-07 -> ['121,124(again),125,128,133(again)', '100,102,104,105(again)', '73,76,79(again),91,25', '20,21,23,33(again)']
 2024-03-06 -> ['100,102,104,105(again)', '73,76,79(again),91,25', '55(again),56,62,70', '1,3,5,4,19']
diff --git a/doc/cheatsheet/linked_list.md b/doc/cheatsheet/linked_list.md
index 6b071077..3888162b 100644
--- a/doc/cheatsheet/linked_list.md
+++ b/doc/cheatsheet/linked_list.md
@@ -362,7 +362,7 @@ class Solution(object):
 // iteration
 //---------------------------
 // LC 206
-// algorithm book (labu) p.297
+// V0
 public ListNode reverseList(ListNode head) {
 
     if (head == null) {
@@ -372,6 +372,17 @@ public ListNode reverseList(ListNode head) {
     ListNode _prev = null;
 
     while (head != null) {
+        /**
+         *  NOTE !!!!
+         *
+         *   4 operations
+         *
+         *    step 1) cache next
+         *    step 2) point cur to prev
+         *    step 3) move prev to cur
+         *    step 4) move cur to next
+         *
+         */
         ListNode _next = head.next;
         head.next = _prev;
         _prev = head;
@@ -394,15 +405,8 @@ public ListNode reverseList(ListNode head) {
 // algorithm book (labu) p.290
 // IDEA : Recursive
 // https://leetcode.com/problems/reverse-linked-list/editorial/
-public ListNode reverseList_3(ListNode head) {
-    if (head == null || head.next == null) {
-        return head;
-    }
-    ListNode p = reverseList_3(head.next);
-    head.next.next = head;
-    head.next = null;
-    return p;
-}
+// https://github.com/yennanliu/CS_basics/blob/master/leetcode_java/src/main/java/LeetCodeJava/LinkedList/ReverseLinkedList.java
+// same as above 
 ```
 
 #### 1-1-5) Reverse *nodes in [a,b]*  linked list (iteration)
diff --git a/leetcode_java/src/main/java/LeetCodeJava/LinkedList/ReverseLinkedList.java b/leetcode_java/src/main/java/LeetCodeJava/LinkedList/ReverseLinkedList.java
index 7abd80fd..3921eaba 100644
--- a/leetcode_java/src/main/java/LeetCodeJava/LinkedList/ReverseLinkedList.java
+++ b/leetcode_java/src/main/java/LeetCodeJava/LinkedList/ReverseLinkedList.java
@@ -18,6 +18,17 @@ public ListNode reverseList(ListNode head) {
             ListNode _prev = null;
 
             while (head != null) {
+                /**
+                 *  NOTE !!!!
+                 *
+                 *   4 operations
+                 *
+                 *    step 1) cache next
+                 *    step 2) point cur to prev
+                 *    step 3) move prev to cur
+                 *    step 4) move cur to next
+                 *
+                 */
                 ListNode _next = head.next;
                 head.next = _prev;
                 _prev = head;