count-dominant-nodes-in-a-binary-tree

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Algorithms

You are given the <code>root</code> of a complete binary tree.

A node <code>x</code> is called dominant if its value is equal to the maximum value among all nodes in the subtree rooted at <code>x</code>.

Return the number of dominant nodes in the tree.

&nbsp;
Example 1:

<div class="example-block">
<img alt="" src="https://assets.leetcode.com/uploads/2026/06/13/tnew.png" style="width: 300px; height: 193px;" />

Input: root = [5,3,8,2,4,7,1]

Output: 5

Explanation:

<ul>
	<li>The leaf nodes with values 2, 4, 7, and 1 are dominant.</li>
	<li>The node with value 8 is dominant because its value is the maximum value in its subtree <code>[8, 7, 1]</code>.</li>
	<li>Thus, the answer is 5.</li>
</ul>
</div>

Example 2:

<div class="example-block">
<img alt="" src="https://assets.leetcode.com/uploads/2026/06/15/t9.png" style="width: 250px; height: 183px;" />

Input: root = [1,2,3,1,2]

Output: 4

Explanation:

<ul>
	<li>The leaf nodes with values 1, 2, and 3 are dominant.</li>
	<li>The node with value 2 whose subtree is <code>[2, 1, 2]</code> is dominant because its value is the maximum value in its subtree.</li>
	<li>Thus, the answer is 4.</li>
</ul>
</div>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 105]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 109</code></li>
	<li>The tree is guaranteed to be a complete binary tree.</li>
</ul>