一、题目内容

二、题解

解法1：

思路

快慢指针找中点后逆序后半部分，拼接链表

代码

public class Solution {
    public void reorderList(ListNode head) {
        if(head == null||head.next == null||head.next.next == null){
            return;
        }
        ListNode fast = head,slow = head;
        while(fast!=null && fast.next!=null){
            fast = fast.next.next;
            slow = slow.next;
        }
        ListNode next = slow.next;
        slow.next = null;
        ListNode newStart = reverse(next);
        slow = head;
        while(slow!=null&&newStart!=null){
            ListNode slowNext = slow.next;
            slow.next = null;
            ListNode newStartNext = newStart.next;
            newStart.next = null;
            slow.next = newStart;
            newStart.next = slowNext;
            slow = slow.next.next;
            newStart = newStartNext;
        }
    }
    private ListNode reverse(ListNode root){
        if(root.next == null){
            return root;
        }
        ListNode pre = null;
        ListNode cur = root;
        while(cur!=null){
            ListNode next = cur.next;
            cur.next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }
}