Project Notes

Flatten Binary Tree to Linked List

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Description

tab: English
 
<p>Given the <code>root</code> of a binary tree, flatten the tree into a &quot;linked list&quot;:</p>
 
<ul>
	<li>The &quot;linked list&quot; should use the same <code>TreeNode</code> class where the <code>right</code> child pointer points to the next node in the list and the <code>left</code> child pointer is always <code>null</code>.</li>
	<li>The &quot;linked list&quot; should be in the same order as a <a href="https://en.wikipedia.org/wiki/Tree_traversal#Pre-order,_NLR" target="_blank"><strong>pre-order</strong><strong> traversal</strong></a> of the binary tree.</li>
</ul>
 
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/14/flaten.jpg" style="width: 500px; height: 226px;" />
<pre>
<strong>Input:</strong> root = [1,2,5,3,4,null,6]
<strong>Output:</strong> [1,null,2,null,3,null,4,null,5,null,6]
</pre>
 
<p><strong class="example">Example 2:</strong></p>
 
<pre>
<strong>Input:</strong> root = []
<strong>Output:</strong> []
</pre>
 
<p><strong class="example">Example 3:</strong></p>
 
<pre>
<strong>Input:</strong> root = [0]
<strong>Output:</strong> [0]
</pre>
 
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>
 
<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 2000]</code>.</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</code></li>
</ul>
 
<p>&nbsp;</p>
<strong>Follow up:</strong> Can you flatten the tree in-place (with <code>O(1)</code> extra space)?
 
 
> [!tip]- Hint 1
> 
> If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.
 
 
---
 
[submissions](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/submissions/) | [solutions](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/solutions/)
 
 
tab: 中文
 
<p>给你二叉树的根结点 <code>root</code> ，请你将它展开为一个单链表：</p>
 
<ul>
	<li>展开后的单链表应该同样使用 <code>TreeNode</code> ，其中 <code>right</code> 子指针指向链表中下一个结点，而左子指针始终为 <code>null</code> 。</li>
	<li>展开后的单链表应该与二叉树 <a href="https://baike.baidu.com/item/%E5%85%88%E5%BA%8F%E9%81%8D%E5%8E%86/6442839?fr=aladdin" target="_blank"><strong>先序遍历</strong></a> 顺序相同。</li>
</ul>
 
<p> </p>
 
<p><strong>示例 1：</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/14/flaten.jpg" style="width: 500px; height: 226px;" />
<pre>
<strong>输入：</strong>root = [1,2,5,3,4,null,6]
<strong>输出：</strong>[1,null,2,null,3,null,4,null,5,null,6]
</pre>
 
<p><strong>示例 2：</strong></p>
 
<pre>
<strong>输入：</strong>root = []
<strong>输出：</strong>[]
</pre>
 
<p><strong>示例 3：</strong></p>
 
<pre>
<strong>输入：</strong>root = [0]
<strong>输出：</strong>[0]
</pre>
 
<p> </p>
 
<p><strong>提示：</strong></p>
 
<ul>
	<li>树中结点数在范围 <code>[0, 2000]</code> 内</li>
	<li><code>-100 <= Node.val <= 100</code></li>
</ul>
 
<p> </p>
 
<p><strong>进阶：</strong>你可以使用原地算法（<code>O(1)</code> 额外空间）展开这棵树吗？</p>
 
 
 
> [!tip]- 提示 1
> 
> If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.
 
 
---
 
[提交记录](https://leetcode.cn/problems/flatten-binary-tree-to-linked-list/submissions/) | [题解](https://leetcode.cn/problems/flatten-binary-tree-to-linked-list/solution/)

Solutions & Notes

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