Lintcode-medium-reorder List

Given a singly linked list l:l0→l1→ ... →ln-1→ln

Reorder It to:l0→ln→l1→ln-1→l2→ln-2→ ...

Example

Given 1->2->3->4->null , reorder it to 1->4->2->3->null .

Challenge

Can do this in-place without altering the nodes ' values?

/*** Definition for ListNode. * public class ListNode {* int val; * ListNode Next; * ListNode (int val) {* This.val = val; * This.next = null; *     } * } */  Public classSolution {/**     * @paramhead:the head of linked list. * @return: void*/     Public voidreorderlist (ListNode head) {//Write your code here                if(Head = =NULL|| Head.next = =NULL|| Head.next.next = =NULL)            return; ListNode Slow=Head; ListNode Fast=Head;  while(Fast! =NULL&& Fast.next! =NULL&& Fast.next.next! =NULL) {Slow=Slow.next; Fast=Fast.next.next; } ListNode head2=Slow.next; Slow.next=NULL; Head2=reverse (head2); ListNode P1=Head; ListNode P2=head2; ListNode P1_next=Head.next; ListNode P2_next=Head2.next;  while(P1_next! =NULL&& P2_next! =NULL) {P1.next=P2; P2.next=P1_next; P1=P1_next; P2=P2_next; P1_next=P1_next.next; P2_next=P2_next.next; } P1.next=P2; P2.next=P1_next; return; }         PublicListNode Reverse (listnode head) {if(Head = =NULL|| Head.next = =NULL)            returnHead; ListNode prev=Head; ListNode Curr=Head.next; ListNode Next=Head.next.next; Head.next=NULL;  while(Next! =NULL) {Curr.next=prev; Prev=Curr; Curr=Next; Next=Next.next; } Curr.next=prev; returnCurr; }}

Lintcode-medium-reorder List