重构“字符串”这章

Author: soulmachine

C++/LeetCodet题解(C++版).pdf

@@ -2271,7 +2271,38 @@ \subsubsection{分析}
 \subsubsection{代码}
 \begin{Code}
 // LeetCode, Reverse Nodes in k-Group
-// 时间复杂度O(n)，空间复杂度O(1)
+// 递归版，时间复杂度O(n)，空间复杂度O(1)
+class Solution {
+public:
+    ListNode *reverseKGroup(ListNode *head, int k) {
+        if (head == nullptr || head->next == nullptr || k < 2)
+            return head;
+
+        ListNode *next_group = head;
+        for (int i = 0; i < k; ++i) {
+            if (next_group)
+                next_group = next_group->next;
+            else
+                return head;
+        }
+        // next_group is the head of next group
+        // new_next_group is the new head of next group after reversion
+        ListNode *new_next_group = reverseKGroup(next_group, k);
+        ListNode *prev = NULL, *cur = head;
+        while (cur != next_group) {
+            ListNode *next = cur->next;
+            cur->next = prev ? prev : new_next_group;
+            prev = cur;
+            cur = next;
+        }
+        return prev; // prev will be the new head of this group
+    }
+};
+\end{Code}
+
+\begin{Code}
+// LeetCode, Reverse Nodes in k-Group
+// 迭代版，时间复杂度O(n)，空间复杂度O(1)
 class Solution {
 public:
     ListNode *reverseKGroup(ListNode *head, int k) {
@@ -2330,7 +2361,7 @@ \subsubsection{分析}
 \subsubsection{代码}
 \begin{Code}
 // LeetCode, Copy List with Random Pointer
-// 两遍扫描
+// 两遍扫描，时间复杂度O(n)，空间复杂度O(1)
 class Solution {
 public:
     RandomListNode *copyRandomList(RandomListNode *head) {