mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
synced 2025-11-04 11:43:12 +08:00
34 lines
1.4 KiB
HTML
34 lines
1.4 KiB
HTML
<p>Given the <code>root</code> of a binary tree, <em>determine if it is a valid binary search tree (BST)</em>.</p>
|
|
|
|
<p>A <strong>valid BST</strong> is defined as follows:</p>
|
|
|
|
<ul>
|
|
<li>The left <span data-keyword="subtree">subtree</span> of a node contains only nodes with keys <strong>less than</strong> the node's key.</li>
|
|
<li>The right subtree of a node contains only nodes with keys <strong>greater than</strong> the node's key.</li>
|
|
<li>Both the left and right subtrees must also be binary search trees.</li>
|
|
</ul>
|
|
|
|
<p> </p>
|
|
<p><strong class="example">Example 1:</strong></p>
|
|
<img alt="" src="https://assets.leetcode.com/uploads/2020/12/01/tree1.jpg" style="width: 302px; height: 182px;" />
|
|
<pre>
|
|
<strong>Input:</strong> root = [2,1,3]
|
|
<strong>Output:</strong> true
|
|
</pre>
|
|
|
|
<p><strong class="example">Example 2:</strong></p>
|
|
<img alt="" src="https://assets.leetcode.com/uploads/2020/12/01/tree2.jpg" style="width: 422px; height: 292px;" />
|
|
<pre>
|
|
<strong>Input:</strong> root = [5,1,4,null,null,3,6]
|
|
<strong>Output:</strong> false
|
|
<strong>Explanation:</strong> The root node's value is 5 but its right child's value is 4.
|
|
</pre>
|
|
|
|
<p> </p>
|
|
<p><strong>Constraints:</strong></p>
|
|
|
|
<ul>
|
|
<li>The number of nodes in the tree is in the range <code>[1, 10<sup>4</sup>]</code>.</li>
|
|
<li><code>-2<sup>31</sup> <= Node.val <= 2<sup>31</sup> - 1</code></li>
|
|
</ul>
|