mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
synced 2025-11-04 03:33:12 +08:00
39 lines
1.4 KiB
HTML
39 lines
1.4 KiB
HTML
<p>Given the <code>root</code> of a binary tree, flatten the tree into a "linked list":</p>
|
|
|
|
<ul>
|
|
<li>The "linked list" 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 "linked list" 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> </p>
|
|
<p><strong>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>Example 2:</strong></p>
|
|
|
|
<pre>
|
|
<strong>Input:</strong> root = []
|
|
<strong>Output:</strong> []
|
|
</pre>
|
|
|
|
<p><strong>Example 3:</strong></p>
|
|
|
|
<pre>
|
|
<strong>Input:</strong> root = [0]
|
|
<strong>Output:</strong> [0]
|
|
</pre>
|
|
|
|
<p> </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 <= Node.val <= 100</code></li>
|
|
</ul>
|
|
|
|
<p> </p>
|
|
<strong>Follow up:</strong> Can you flatten the tree in-place (with <code>O(1)</code> extra space)? |