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814. Binary Tree Pruning

Difficulty Topics

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.

Solution

binary-tree-pruning.py
# 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]:

        def dfs(node):
            if not node: return None

            node.left = dfs(node.left)
            node.right = dfs(node.right)

            if node.val == 0 and not node.left and not node.right: return None

            return node

        return dfs(root)