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Java-based LeetCode algorithm problem solutions, regularly updated
814\. Binary Tree Pruning
Medium
Given the `root` of a binary tree, return _the same tree where every subtree (of the given tree) not containing a_ `1` _has been removed_.
A subtree of a node `node` is `node` plus every node that is a descendant of `node`.
**Example 1:**
![](https://s3-lc-upload.s3.amazonaws.com/uploads/2018/04/06/1028_2.png)
**Input:** root = [1,null,0,0,1]
**Output:** [1,null,0,null,1]
**Explanation:** Only the red nodes satisfy the property "every subtree not containing a 1". The diagram on the right represents the answer.
**Example 2:**
![](https://s3-lc-upload.s3.amazonaws.com/uploads/2018/04/06/1028_1.png)
**Input:** root = [1,0,1,0,0,0,1]
**Output:** [1,null,1,null,1]
**Example 3:**
![](https://s3-lc-upload.s3.amazonaws.com/uploads/2018/04/05/1028.png)
**Input:** root = [1,1,0,1,1,0,1,0]
**Output:** [1,1,0,1,1,null,1]
**Constraints:**
* The number of nodes in the tree is in the range `[1, 200]`.
* `Node.val` is either `0` or `1`.