328. 奇偶链表

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode oddEvenList(ListNode head) {
        if (head == null || head.next == null) return head;
       
        ListNode odd = head;
        ListNode even = head.next;
        int cnt = 1;
        ListNode curr = even.next;
        even.next = null;
        while(curr != null){
            ListNode tmp = curr;
            curr = curr.next;
            if(cnt == 1){
                tmp.next  = odd.next;
                odd.next = tmp;
                odd = tmp;
                cnt--;
            }else {
                tmp.next  = even.next;
                even.next = tmp;
                even = tmp;
                cnt++;
            } 
        }
        return head;
    }
}