> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/trees/binary-tree-pruning.md).

# Binary Tree Pruning

We are given the head node `root` of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

```
Example 1:
Input: [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:
Input: [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]



```

```
Example 3:
Input: [1,1,0,1,1,0,1,0]
Output: [1,1,0,1,1,null,1]



```

**Note:**

* The binary tree will have at most `100 nodes`.
* The value of each node will only be `0` or `1`.

```java
class Solution {
    public TreeNode pruneTree(TreeNode root) {
        if (root == null)
            return root;
        if (root.left == null && root.right == null) {
            if (root.val == 0)
                return null;
            return root;
        }
        root.left = pruneTree(root.left);
        root.right = pruneTree(root.right);
        if (root.left == null && root.right == null && root.val == 0)
            return null;
        return root;
    }
}
```