LC 0814 [M] Binary Tree Pruning - ALawliet/algorithms GitHub Wiki

# 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 postorder(node):
            if not node:
                return 0
            
            L = postorder(node.left)
            R = postorder(node.right)
            
            # print(f'{L}/{node.val}\{R}')
            if L == 0:
                node.left = None
            if R == 0:
                node.right = None
            
            return L + R + node.val
        
        postorder(root)
        
        '''
        edge case
        Input: [0,null,0,0,0]
        Output: [0]
        Expected: []
        '''
        if not root.left and not root.right and root.val == 0:
            return None
        
        return root

def pruneTree(self, root):
        if not root: return None
        root.left = self.pruneTree(root.left)
        root.right = self.pruneTree(root.right)
        if not root.left and not root.right and not root.val: return None
        return root

class Solution:
    def pruneTree(self, root):
        def dfs(node):
            if not node: return True
            left, right = dfs(node.left), dfs(node.right)
            if left: node.left = None
            if right: node.right = None
            return left and right and node.val == 0
        
        return root if not dfs(root) else None