Project Notes

Count Complete Tree Nodes

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Description

tab: English
 
<p>Given the <code>root</code> of a <strong>complete</strong> binary tree, return the number of the nodes in the tree.</p>
 
<p>According to <strong><a href="http://en.wikipedia.org/wiki/Binary_tree#Types_of_binary_trees" target="_blank">Wikipedia</a></strong>, every level, except possibly the last, is completely filled in a complete binary tree, and all nodes in the last level are as far left as possible. It can have between <code>1</code> and <code>2<sup>h</sup></code> nodes inclusive at the last level <code>h</code>.</p>
 
<p>Design an algorithm that runs in less than&nbsp;<code data-stringify-type="code">O(n)</code>&nbsp;time complexity.</p>
 
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/14/complete.jpg" style="width: 372px; height: 302px;" />
<pre>
<strong>Input:</strong> root = [1,2,3,4,5,6]
<strong>Output:</strong> 6
</pre>
 
<p><strong class="example">Example 2:</strong></p>
 
<pre>
<strong>Input:</strong> root = []
<strong>Output:</strong> 0
</pre>
 
<p><strong class="example">Example 3:</strong></p>
 
<pre>
<strong>Input:</strong> root = [1]
<strong>Output:</strong> 1
</pre>
 
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>
 
<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 5 * 10<sup>4</sup>]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 5 * 10<sup>4</sup></code></li>
	<li>The tree is guaranteed to be <strong>complete</strong>.</li>
</ul>
 
 
 
---
 
[submissions](https://leetcode.com/problems/count-complete-tree-nodes/submissions/) | [solutions](https://leetcode.com/problems/count-complete-tree-nodes/solutions/)
 
 
tab: 中文
 
<p>给你一棵<strong> 完全二叉树</strong> 的根节点 <code>root</code> ，求出该树的节点个数。</p>
 
<p><a href="https://baike.baidu.com/item/%E5%AE%8C%E5%85%A8%E4%BA%8C%E5%8F%89%E6%A0%91/7773232?fr=aladdin">完全二叉树</a> 的定义如下：在完全二叉树中，除了最底层节点可能没填满外，其余每层节点数都达到最大值，并且最下面一层的节点都集中在该层最左边的若干位置。若最底层为第 <code>h</code> 层（从第 0 层开始），则该层包含 <code>1~&nbsp;2<sup>h</sup></code>&nbsp;个节点。</p>
 
<p>&nbsp;</p>
 
<p><strong>示例 1：</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/14/complete.jpg" style="width: 372px; height: 302px;" />
<pre>
<strong>输入：</strong>root = [1,2,3,4,5,6]
<strong>输出：</strong>6
</pre>
 
<p><strong>示例 2：</strong></p>
 
<pre>
<strong>输入：</strong>root = []
<strong>输出：</strong>0
</pre>
 
<p><strong>示例 3：</strong></p>
 
<pre>
<strong>输入：</strong>root = [1]
<strong>输出：</strong>1
</pre>
 
<p>&nbsp;</p>
 
<p><strong>提示：</strong></p>
 
<ul>
	<li>树中节点的数目范围是<code>[0, 5 * 10<sup>4</sup>]</code></li>
	<li><code>0 &lt;= Node.val &lt;= 5 * 10<sup>4</sup></code></li>
	<li>题目数据保证输入的树是 <strong>完全二叉树</strong></li>
</ul>
 
<p>&nbsp;</p>
 
<p><strong>进阶：</strong>遍历树来统计节点是一种时间复杂度为 <code>O(n)</code> 的简单解决方案。你可以设计一个更快的算法吗？</p>
 
 
 
---
 
[提交记录](https://leetcode.cn/problems/count-complete-tree-nodes/submissions/) | [题解](https://leetcode.cn/problems/count-complete-tree-nodes/solution/)

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