leetcode：814. Binary tree pruning [DFS]

analysis

Find the whole subtree 0 Of kill fall

ac code

# 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]:
        # check Is it all 0
        def check(node):
            if not node:
                return True
            if node.left is None and node.right is None and node.val == 0:
                return True
            if node.left is None and node.right is None and node.val == 1:
                return False

            return node.val == 0 and check(node.left) and check(node.right)
        
        def change(node):
            if check(node):
                return None
            if node.left: node.left = change(node.left)
            if node.right: node.right = change(node.right)
            return node
        

        return change(root)

summary

Simple check + change