<Prove safety offer> 13 title

topic:

After the head node is defined a function, a list of input, output and inverting the inverted list of list head node

Ideas:

(1) stored at a current node

(2) points to the next reversal of the current node, a node point

(3) updating the current node pre

(4) the current node to the next node

Code:

public class Thirdteenth {
    class ListNode{
        ListNode next;
        int val;
    }
    public static ListNode reverseList(ListNode head){
        if (head == null){
            return null;
        }
        ListNode cur = head;
        ListNode pre = null;
        while(cur != null){
            ListNode temp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
}