814-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]:
        root = self.DFS(root)
        return root
    
    def DFS(self, root):
        if not root:
            return
    
        root.left = self.DFS(root.left)
        root.right = self.DFS(root.right)
        
        if root.val == 0 and root.left is None and root.right is None:
            return None
        else:
            return root