LCR 026. 重排链表

/**
 * 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 void reorderList(ListNode head) {
        ListNode fast = head.next, slow = head;
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }
        ListNode tmp = slow.next;
        slow.next = null;
        while (tmp != null) {
            ListNode tmp2 = tmp.next;
            tmp.next = slow.next;
            slow.next = tmp;
            tmp = tmp2;
        }
        tmp = slow.next;
        slow.next = null;
        fast=head;
        while(tmp!=null){
            ListNode tmp2 = tmp.next;
            ListNode tmp3 = fast.next;
            tmp.next = fast.next;
            fast.next = tmp;
            fast=tmp3;
            tmp=tmp2;
        }

        // ListNode tmp4 = head;
        // while (tmp4 != null) {
        //     System.out.println(tmp4.val);
        //     tmp4 = tmp4.next;
        // }
    }
}