[LeetCode]--25. Reverse Nodes in k-Group

See the answer code!

/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ public class Solution { public ListNode reverseKGroup(ListNode head, int k) { ListNode curr = head; int count = 0; while (curr != null && count != k) { curr = curr.next; count++; } if (count == k) { curr = reverseKGroup(curr, k); while (count-- > 0) { ListNode tmp = head.next; head.next = curr; curr = head; head = tmp; } head = curr; } return head; } } public class Solution { public ListNode reverseKGroup(ListNode head, int k) { if (head==null||head.next==null||k<2) return head; ListNode dummy = new ListNode(0); dummy.next = head; ListNode tail = dummy, prev = dummy,temp; int count; while(true){ count =k; while(count>0&&tail!=null){ count--; tail=tail.next; } if (tail==null) break;//Has reached the end head=prev.next;//for next cycle // prev-->temp-->...--->....--->tail-->.... // Delete @temp and insert to the next position of @tail // prev-->...-->...-->tail-->head-->... // Assign @temp to the next node of @prev // prev-->temp-->...-->tail-->...-->... // Keep doing until @tail is the next node of @prev while(prev.next!=tail){ temp=prev.next;//Assign prev.next=temp.next;//Delete temp.next=tail.next; tail.next=temp;//Insert } tail=head; prev=head; } return dummy.next; } }

Reference

https://discuss.leetcode.com/category/33/reverse-nodes-in-k-group https://discuss.leetcode.com/topic/7126/short-but-recursive-java-code-with-comments https://discuss.leetcode.com/topic/5604/share-my-java-solution-with-comments-in-line