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"title": "展平多级双向链表",
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"content": "<p>English description is not available for the problem. Please switch to Chinese.</p>\n",
"translatedTitle": "展平多级双向链表",
"translatedContent": "<p>多级双向链表中，除了指向下一个节点和前一个节点指针之外，它还有一个子链表指针，可能指向单独的双向链表。这些子列表也可能会有一个或多个自己的子项，依此类推，生成多级数据结构，如下面的示例所示。</p>\n\n<p>给定位于列表第一级的头节点，请扁平化列表，即将这样的多级双向链表展平成普通的双向链表，使所有结点出现在单级双链表中。</p>\n\n<p> </p>\n\n<p><strong>示例 1：</strong></p>\n\n<pre>\n<strong>输入：</strong>head = [1,2,3,4,5,6,null,null,null,7,8,9,10,null,null,11,12]\n<strong>输出：</strong>[1,2,3,7,8,11,12,9,10,4,5,6]\n<strong>解释：\n</strong>\n输入的多级列表如下图所示：\n\n<img src=\"https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/10/12/multilevellinkedlist.png\" style=\"height: 363px; width: 640px;\" />\n\n扁平化后的链表如下图：\n\n<img src=\"https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/10/12/multilevellinkedlistflattened.png\" style=\"height: 80px; width: 1100px;\" />\n</pre>\n\n<p><strong>示例 2：</strong></p>\n\n<pre>\n<strong>输入：</strong>head = [1,2,null,3]\n<strong>输出：</strong>[1,3,2]\n<strong>解释：\n\n</strong>输入的多级列表如下图所示：\n\n 1---2---NULL\n |\n 3---NULL\n</pre>\n\n<p><strong>示例 3：</strong></p>\n\n<pre>\n<strong>输入：</strong>head = []\n<strong>输出：</strong>[]\n</pre>\n\n<p> </p>\n\n<p><strong>如何表示测试用例中的多级链表？</strong></p>\n\n<p>以 <strong>示例 1</strong> 为例：</p>\n\n<pre>\n 1---2---3---4---5---6--NULL\n |\n 7---8---9---10--NULL\n |\n 11--12--NULL</pre>\n\n<p>序列化其中的每一级之后：</p>\n\n<pre>\n[1,2,3,4,5,6,null]\n[7,8,9,10,null]\n[11,12,null]\n</pre>\n\n<p>为了将每一级都序列化到一起，我们需要每一级中添加值为 null 的元素，以表示没有节点连接到上一级的上级节点。</p>\n\n<pre>\n[1,2,3,4,5,6,null]\n[null,null,7,8,9,10,null]\n[null,11,12,null]\n</pre>\n\n<p>合并所有序列化结果，并去除末尾的 null 。</p>\n\n<pre>\n[1,2,3,4,5,6,null,null,null,7,8,9,10,null,null,11,12]</pre>\n\n<p> </p>\n\n<p><strong>提示：</strong></p>\n\n<ul>\n\t<li>节点数目不超过 <code>1000</code></li>\n\t<li><code>1 <= Node.val <= 10^5</code></li>\n</ul>\n\n<p> </p>\n\n<p><meta charset=\"UTF-8\" />注意：本题与主站 430 题相同： <a href=\"https://leetcode-cn.com/problems/flatten-a-multilevel-doubly-linked-list/\">https://leetcode-cn.com/problems/flatten-a-multilevel-doubly-linked-list/</a></p>\n",
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