剑指offerJZ15——反转链表。leetcode206.反转链表

//双指针迭代法
    public ListNode reverseList(ListNode head) {
        ListNode previous = null;
        ListNode current = head;
        while (current != null){
            //记录当前节点的下一个节点
            ListNode temp = current.next;
            //将当前节点指向previous，相等与把当前节点反转
            current.next = previous;
            //分别前进一个节点
            previous = current;
            current = temp;
        }
        //最后previous指向原链表的最后一个节点，反转后的第一个节点
        return previous;
    }