leetcode-problemset/leetcode/problem/delete-leaves-with-a-given-value.html

<p>Given a binary tree <code>root</code> and an integer <code>target</code>, delete all the <strong>leaf nodes</strong> with value <code>target</code>.</p>

<p>Note that once you delete a leaf node with value <code>target</code><strong>, </strong>if its parent node becomes a leaf node and has the value <code>target</code>, it should also be deleted (you need to continue doing that until you cannot).</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/01/09/sample_1_1684.png" style="width: 500px; height: 112px;" /></strong></p>

<pre>
<strong>Input:</strong> root = [1,2,3,2,null,2,4], target = 2
<strong>Output:</strong> [1,null,3,null,4]
<strong>Explanation:</strong> Leaf nodes in green with value (target = 2) are removed (Picture in left). 
After removing, new nodes become leaf nodes with value (target = 2) (Picture in center).
</pre>

<p><strong class="example">Example 2:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/01/09/sample_2_1684.png" style="width: 400px; height: 154px;" /></strong></p>

<pre>
<strong>Input:</strong> root = [1,3,3,3,2], target = 3
<strong>Output:</strong> [1,3,null,null,2]
</pre>

<p><strong class="example">Example 3:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/01/15/sample_3_1684.png" style="width: 500px; height: 166px;" /></strong></p>

<pre>
<strong>Input:</strong> root = [1,2,null,2,null,2], target = 2
<strong>Output:</strong> [1]
<strong>Explanation:</strong> Leaf nodes in green with value (target = 2) are removed at each step.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 3000]</code>.</li>
	<li><code>1 &lt;= Node.val, target &lt;= 1000</code></li>
</ul>