/*
 * @lc app=leetcode id=328 lang=java
 *
 * [328] Odd Even Linked List
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode oddEvenList(ListNode head) {
        if(head == null || head.next == null) {
            return head;
        }
        ListNode oddDummy = new ListNode(0), oddTail = oddDummy, evenDummy = new ListNode(0), evenTail = evenDummy, cur = head;
        int i = 1;
        while(cur != null) {
            if(i % 2 == 1) {
                oddTail.next = cur;
                cur = cur.next;
                oddTail = oddTail.next;
                oddTail.next = null;
            } else {
                evenTail.next = cur;
                cur = cur.next;
                evenTail = evenTail.next;
                evenTail.next = null;
            }
            i++;
        }
        oddTail.next = evenDummy.next;
        return oddDummy.next;
    }
}
// @lc code=end