# Binary Tree Pruning Problem

## Description

LeetCode Problem 814.

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:

``````1
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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:

``````1
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Input: root = [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]
``````

Example 3:

``````1
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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.

## Sample C++ Code

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/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode() : val(0), left(nullptr), right(nullptr) {}
*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
TreeNode* pruneTree(TreeNode* root) {
if (root == NULL)
return NULL;

if (root->left != NULL) {
root->left = pruneTree(root->left);
}
if (root->right != NULL) {
root->right = pruneTree(root->right);
}
if ((root->left == NULL) && (root->right == NULL)) {
if (root->val == 0)
return NULL;
else
return root;
}
return root;
}
};
``````