每天1题算法题（6）- 反转链表（√）

反转一个单链表。

 解答

class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null) {
            return head;
        }
        List<ListNode> list = new ArrayList();
        while(head != null) {
            list.add(head);
            ListNode tmpNode = head.next;
            head.next = null;
            head = tmpNode;
        }
        ListNode newHead = null;
        ListNode curHead = null;
        for(int i = list.size()-1;i>=0;i--) {
            ListNode tmpNode = list.get(i);
            if(newHead == null) {
                newHead = tmpNode;
                curHead = tmpNode;
            } else {
                curHead.next = tmpNode;
                curHead = tmpNode;
            }
        }
        return newHead;
    }
}