## DEV Community

Abhishek Chaudhary

Posted on

# Binary Tree Pruning

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`.

SOLUTION:

``````# 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 hasOne(self, root):
if root:
if root.val == 1:
return True
if self.hasOne(root.left) or self.hasOne(root.right):
return True
return False

def pruneTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
if not self.hasOne(root):
return None
root.left = self.pruneTree(root.left)
root.right = self.pruneTree(root.right)
return root
``````