题目:
Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.
k is 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.
Example:
Given this linked list: 1->2->3->4->5
For k = 2, you should return: 2->1->4->3->5
For k = 3, you should return: 3->2->1->4->5
Note:
Only constant extra memory is allowed.
You may not alter the values in the list's nodes, only nodes itself may be changed.
public class ReverseNodesKGroup {
public ListNode reverseKGroup(ListNode head, int k) {
if(head==null||head.next==null||k==1)
return head;
ListNode dummy = new ListNode(-1);
dummy.next = head;
ListNode last = dummy;
ListNode pre = dummy.next;
int len = getLength(head);
while(len>=k){
for(int i=0;i<(k-1);i++){
ListNode cur = pre.next;
pre.next = cur.next;
cur.next = last.next;
last.next = cur;
}
len =len - k;
last = pre;
pre = pre.next;
}
return dummy.next;
}
public int getLength(ListNode head){
int len = 0;
while(head!=null){
len++;
head = head.next;
}
return len;
}
}