Given a linked list, reverse the nodes of a linked list
kat a time and return its modified list.
kis a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes, in the end, should remain as it is.Follow up:
- Could you solve the problem in
O(1)extra memory space?- You may not alter the values in the list’s nodes, only nodes itself may be changed.
Example:
Input: head = [1,2,3,4,5], k = 2
Output: [2,1,4,3,5]
Input: head = [1,2,3,4,5], k = 3
Output: [3,2,1,4,5]
Input: head = [1,2,3,4,5], k = 1
Output: [1,2,3,4,5]
Input: head = [1], k = 1
Output: [1]
Thoughts
Code(JAVA)
public ListNode reverseKGroup(ListNode head, int k) {
if(head == null || k == 1)
return head;
ListNode dummyHead = new ListNode(0,head);
ListNode prev = dummyHead,cur = head;
int i = 0;
while(cur != null) {
i ++;
if(i % k == 0) {
prev = reverseList(prev,cur.next);
cur = prev.next;
}
else
cur = cur.next;
}
return dummyHead.next;
}
private ListNode reverseList(ListNode prev, ListNode next) {
ListNode last = prev.next;
ListNode cur = last.next;
while(cur != next) {
last.next = cur.next;
cur.next = prev.next;
prev.next = cur;
cur = last.next;
}
return last;
}
