Java实现反转双向链表

class ListNode {
    int val;
    ListNode next;
    ListNode prev;
    ListNode(int x) {
        val = x;
    }
}

class Solution {
    public ListNode reverseList(ListNode head){
        ListNode pre=null;
        ListNode next=null;
        while(head!=null){
            next=head.next;
            head.next=pre;//两个节点的后继节点和前驱节点进行互换
            head.prev=next;
            pre=head;
            head=next;
        }
        return pre;
    }
}