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# 0814. Binary Tree Pruning

<https://leetcode.com/problems/binary-tree-pruning>

## Description

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`.

## ac

```java
```