//定义链表的方法
class ListNode {
				constructor(val){
					this.val =val
					this.next=null
				}
			}
			
			let node1 = new ListNode(1)
			let node2 = new ListNode(2)
			let node3 = new ListNode(3)
			node1.next =node2
			node2.next =node3
//反转链表
console.log(node1)
function reverse(head){
				let  dummy=head;
				let tmp=dummy;
				
				while(head !==null&&head.next !==null){
					dummy = head.next
					head.next =dummy.next
					dummy.next=tmp
					tmp=dummy

				}
				return dummy
			}
			
				console.log(reverse(node1))