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• /**

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.

*/

public class Binary_Tree_Pruning {

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

root.left = pruneTree(root.left);
root.right = pruneTree(root.right);

// leaf node
if (root.left == null && root.right == null) {
if (root.val == 0) {
return null;
} else {
return root;
}
}

return root;
}
}
}

############

/**
* 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;
}
}


• // OJ: https://leetcode.com/problems/binary-tree-pruning/
// Time: O(N)
// Space: O(logN)
class Solution {
public:
TreeNode* pruneTree(TreeNode* root) {
if (!root) return NULL;
root->left = pruneTree(root->left);
root->right = pruneTree(root->right);
return root->left || root->right || root->val ? root : NULL;
}
};

• # 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.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def pruneTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
if not root: return
root.left = self.pruneTree(root.left)
root.right = self.pruneTree(root.right)
if not root.left and not root.right and root.val == 0:
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)
}
}


• /**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode pruneTree(TreeNode root) {
if (root == null)
return root;
Map<TreeNode, TreeNode> childParentMap = new HashMap<TreeNode, TreeNode>();
List<TreeNode> nodesList = new ArrayList<TreeNode>();
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode node = queue.poll();
TreeNode left = node.left, right = node.right;
if (left != null) {
childParentMap.put(left, node);
queue.offer(left);
}
if (right != null) {
childParentMap.put(right, node);
queue.offer(right);
}
}
for (int i = nodesList.size() - 1; i >= 0; i--) {
TreeNode node = nodesList.get(i);
if (node.val == 0) {
if (node.left == null && node.right == null) {
TreeNode parent = childParentMap.get(node);
if (parent != null) {
if (node == parent.left)
parent.left = null;
else
parent.right = null;
} else {
root = null;
break;
}
}
}
}
return root;
}
}

############

/**
* 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;
}
}


• // OJ: https://leetcode.com/problems/binary-tree-pruning/
// Time: O(N)
// Space: O(logN)
class Solution {
public:
TreeNode* pruneTree(TreeNode* root) {
if (!root) return NULL;
root->left = pruneTree(root->left);
root->right = pruneTree(root->right);
return root->left || root->right || root->val ? root : NULL;
}
};

• # 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.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def pruneTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
if not root: return
root.left = self.pruneTree(root.left)
root.right = self.pruneTree(root.right)
if not root.left and not root.right and root.val == 0:
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)
}
}