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Use an iterative approach to reverse each group of k nodes separately. This approach leverages an auxiliary dummy node and previous and current pointers to manage the connections at each step. We traverse the list, checking for complete sets of k nodes to reverse them. If a group of nodes has less than k nodes, leave them as they are.
Time Complexity: O(n), where n is the number of nodes in the list, as each node is processed once.
Space Complexity: O(1), since no extra space is used apart from pointers.
1public class ListNode {
2 public int val;
3 public ListNode next;
4 public ListNode(int x) { val = x; }
5}
6
7public class Solution {
8 public ListNode ReverseKGroup(ListNode head, int k) {
9 if (head == null || k == 1) return head;
10 ListNode dummy = new ListNode(0) { next = head };
11 ListNode prev = dummy, current = head;
12
13 int len = 0;
14 while (current != null)
15 {
16 len++;
17 current = current.next;
18 }
19
20 while (len >= k) {
21 current = prev.next;
22 ListNode next = current.next;
23 for (int i = 1; i < k; ++i) {
24 current.next = next.next;
25 next.next = prev.next;
26 prev.next = next;
27 next = current.next;
28 }
29 prev = current;
30 len -= k;
31 }
32 return dummy.next;
33 }
34}
35The C# code utilizes a dummy node for managing connections between sections of the list. Length counting determines the capability of executing k-sized reversals, performed by adjusting node pointers accordingly within each eligible group.
Recurse through the linked list, reversing k nodes at a time. If a full group of k nodes is found, reverse and connect through recursive calls. Terminate when fewer than k nodes are left. This approach inherently uses the call stack for management of reverse sequences.
Time Complexity: O(n), since we process each node once even recursively.
Space Complexity: O(n/k), the recursion depth in worst case equals the number of complete k-sized groups.
1
The recursive JavaScript solution inverts k-segments. Completing reversals, segments are compounded to a final list through recursions collapsing backward, observing terminal convergence for incomplete collections.