vault backup: 2022-09-20 13:28:10

OJ notes/pages/Leetcode Reverse-Linked-List.md

@@ -122,17 +122,32 @@ public:
 
 Recursion:
 
+2022-09-20 version
+```cpp
+class Solution {
+public:
+  ListNode *reverseList(ListNode *head) {
+    // Recursion
+
+    // Base case: no need to reverse:
+    if (head == nullptr || head->next == nullptr) {
+      return head;
+    }
+
+    // assuming we have the head of reversed sub-list
+    // head->next still points to next one in the unchanged order,
+    // or the tail of the reversed list
+    auto newHead = reverseList(head->next);
+
+    head->next->next = head;
+    head->next = nullptr;
+
+    return newHead;
+  }
+};
+```
+
 ```cpp
-/**
- * Definition for singly-linked list.
- * struct ListNode {
- *     int val;
- *     ListNode *next;
- *     ListNode() : val(0), next(nullptr) {}
- *     ListNode(int x) : val(x), next(nullptr) {}
- *     ListNode(int x, ListNode *next) : val(x), next(next) {}
- * };
- */
 class Solution {
 public:
   ListNode *reverseList(ListNode *head) {