328 Odd Even Linked List

Python

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def oddEvenList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        oddDummy = ListNode(-1)
        evenDummy = ListNode(-1)
        oddCur, evenCur = oddDummy, evenDummy
        cnt = 1
        while(head):
            next = head.next
            head.next = None
            if cnt % 2 == 1:
                oddCur.next = head
                oddCur = oddCur.next
            else:
                evenCur.next = head
                evenCur = evenCur.next
            head = next
            cnt += 1 
        oddCur.next = evenDummy.next
        return oddDummy.next

Java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode oddEvenList(ListNode head) {
        int cnt = 1;
        ListNode oddDummy = new ListNode(-1);
        ListNode evenDummy = new ListNode(-1);
        ListNode oddP = oddDummy, evenP = evenDummy;
        while(head != null)
        {
            ListNode next = head.next;
            head.next = null;
            if(cnt % 2 == 0){
                evenP.next = head;
                evenP = evenP.next;
            }
            else{
                oddP.next = head;
                oddP = oddP.next;
            }
            cnt += 1;
            head =  next;
        }
        oddP.next = evenDummy.next;
        return oddDummy.next;    
    }
}