328.奇偶链表.java

/*
 * @lc app=leetcode.cn id=328 lang=java
 *
 * [328] 奇偶链表
 */

// @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) {
            return head;
        }
        // need to store evenHead, after the while, head.next will change and 
        // may not be head of even List
        ListNode odd = head, even = head.next, evenHead = even;
        while(odd.next != null && odd.next.next != null) {
            odd.next = odd.next.next;
            odd = odd.next;
            even.next = even.next.next;
            even = even.next;
        }
        odd.next = evenHead;
        return head;
    }
}
// @lc code=end