Update

include/s0025_reverse_nodes_in_k-group.hpp

@@ -0,0 +1,22 @@
+#ifndef S0025_REVERSE_NODES_IN_K_GROUP
+#define S0025_REVERSE_NODES_IN_K_GROUP
+
+#include <utility>
+#include <tuple>
+
+using namespace std;
+
+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* reverseKGroup(ListNode* head, int k);
+};
+
+#endif

src/s0025_reverse_nodes_in_k-group.cpp

@@ -0,0 +1,44 @@
+#include "s0025_reverse_nodes_in_k-group.hpp"
+
+// 翻转一个子链表，并且返回新的头与尾
+pair<ListNode*, ListNode*> myReverse(ListNode* head, ListNode* tail) {
+  ListNode* prev = tail->next;
+  ListNode* p = head;
+  while (prev != tail) {
+    ListNode* nex = p->next;
+    p->next = prev;
+    prev = p;
+    p = nex;
+  }
+  return {tail, head};
+}
+
+ListNode* Solution::reverseKGroup(ListNode* head, int k) {
+  ListNode* hair = new ListNode(0);
+  hair->next = head;
+  ListNode* pre = hair;
+
+  while (head) {
+    ListNode* tail = pre;
+    // 查看剩余部分长度是否大于等于 k
+    for (int i = 0; i < k; ++i) {
+      tail = tail->next;
+      if (!tail) {
+        return hair->next;
+      }
+    }
+    ListNode* nex = tail->next;
+    // 这里是 C++17 的写法，也可以写成
+    // pair<ListNode*, ListNode*> result = myReverse(head, tail);
+    // head = result.first;
+    // tail = result.second;
+    tie(head, tail) = myReverse(head, tail);
+    // 把子链表重新接回原链表
+    pre->next = head;
+    tail->next = nex;
+    pre = tail;
+    head = tail->next;
+  }
+
+  return hair->next;
+}