206. Reverse Linked List

Reverse a singly linked list.

思路：三指针，一个记录newHead，一个记录curr，一个记录next

    public ListNode reverseList(ListNode head) {
        ListNode newHead = null;
        ListNode curr = head;
        while (curr!=null){
            ListNode next =curr.next;
            curr.next = newHead;
            newHead = curr;
            curr = next;
        }
        return newHead;
    }
}