algorithms/206-reverse-linked-list.ipynb

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    "反转一个单链表。\n",
    "\n",
    "#### 示例:\n",
    "```\n",
    "输入: 1->2->3->4->5->NULL\n",
    "输出: 5->4->3->2->1->NULL\n",
    "```\n",
    "\n",
    "#### 进阶:\n",
    "\n",
    "你可以迭代或递归地反转链表。你能否用两种方法解决这道题？"
   ]
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    "# Definition for singly-linked list.\n",
    "class ListNode:\n",
    "    def __init__(self, val=0, next=None):\n",
    "        self.val = val\n",
    "        self.next = next\n",
    "\n",
    "class Solution:\n",
    "    def reverseList(self, head: ListNode) -> ListNode:\n",
    "        if head == None or head.next == None:\n",
    "            return head\n",
    "        c, n = head, head.next\n",
    "        c.next = None\n",
    "        while n != None:\n",
    "            t = n.next\n",
    "            n.next = c\n",
    "            c = n\n",
    "            n = t\n",
    "            \n",
    "        return c"
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