题解 | #反转链表#

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    
     public ListNode ReverseList(ListNode head) {
        //逻辑短路 所以 不会发生 npe
        if (head == null || head.next==null){
            return head;
        }
        ListNode first = new ListNode(0);
        ListNode cur = head;
        first.next = cur;
        head = head.next;
        first.next.next = null;
        //反转链表采用头插法，即每个节点都在头部插入
        while (head != null){
            cur = head;
            head = head.next;
            cur.next = first.next;
            first.next = cur;
        }
        return first.next;
    }
}