# 814. 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:

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:

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


Example 3:

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.

## Solutions

• /**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode() {}
*     TreeNode(int val) { this.val = val; }
*     TreeNode(int val, TreeNode left, TreeNode right) {
*         this.val = val;
*         this.left = left;
*         this.right = right;
*     }
* }
*/
class Solution {
public TreeNode pruneTree(TreeNode root) {
if (root == null) {
return null;
}
root.left = pruneTree(root.left);
root.right = pruneTree(root.right);
if (root.val == 0 && root.left == null && root.right == null) {
return null;
}
return root;
}
}


• /**
* 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) return nullptr;
root->left = pruneTree(root->left);
root->right = pruneTree(root->right);
if (!root->val && !root->left && !root->right) return nullptr;
return root;
}
};

• # Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def pruneTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
if root is None:
return None
root.left = self.pruneTree(root.left)
root.right = self.pruneTree(root.right)
if root.val == 0 and root.left is None and root.right is None:
return None
return root


• /**
* Definition for a binary tree node.
* type TreeNode struct {
*     Val int
*     Left *TreeNode
*     Right *TreeNode
* }
*/
func pruneTree(root *TreeNode) *TreeNode {
if root == nil {
return nil
}
root.Left = pruneTree(root.Left)
root.Right = pruneTree(root.Right)
if root.Val == 0 && root.Left == nil && root.Right == nil {
return nil
}
return root
}

• /**
* Definition for a binary tree node.
* class TreeNode {
*     val: number
*     left: TreeNode | null
*     right: TreeNode | null
*     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.left = (left===undefined ? null : left)
*         this.right = (right===undefined ? null : right)
*     }
* }
*/

function pruneTree(root: TreeNode | null): TreeNode | null {
if (root == null) {
return root;
}
root.left = pruneTree(root.left);
root.right = pruneTree(root.right);
if (root.val == 0 && root.left == null && root.right == null) {
return null;
}
return root;
}


• /**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
*     this.val = (val===undefined ? 0 : val)
*     this.left = (left===undefined ? null : left)
*     this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {TreeNode} root
* @return {TreeNode}
*/
var pruneTree = function (root) {
if (!root) return null;
root.left = pruneTree(root.left);
root.right = pruneTree(root.right);
if (root.val == 0 && !root.left && !root.right) {
return null;
}
return root;
};


• // Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
//
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;
impl Solution {
pub fn prune_tree(root: Option<Rc<RefCell<TreeNode>>>) -> Option<Rc<RefCell<TreeNode>>> {
if root.is_none() {
return None;
}

let root = root.unwrap();
let left = Self::prune_tree(root.borrow_mut().left.take());
let right = Self::prune_tree(root.borrow_mut().right.take());
if root.borrow().val == 0 && left.is_none() && right.is_none() {
return None;
}

root.borrow_mut().left = left;
root.borrow_mut().right = right;
Some(root)
}
}