Ref: 2 step by step diagrams added.

analysis/04-reverse-linked-list/diagrams/01_save_next.puml

@@ -0,0 +1,38 @@
+@startuml
+title Step 1 — Save next
+
+object "Node 1" as n1 {
+  value = 1
+}
+
+object "Node 2" as n2 {
+  value = 2
+}
+
+object "Node 3" as n3 {
+  value = 3
+}
+
+n1 --> n2 : next
+n2 --> n3 : next
+n3 --> "null" : next
+
+object "previous" as prev
+object "current" as cur
+object "next" as nxt
+
+prev --> "null"
+cur --> n1
+nxt --> n2
+
+note right of nxt
+next = current->next
+
+We save the next node before changing
+current->next.
+
+Without this temporary pointer, the rest
+of the original list would become unreachable.
+end note
+
+@enduml