814. Binary Tree Pruning

We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

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class Solution:
    def pruneTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if not root: return root
        root.left, root.right = self.pruneTree(root.left), self.pruneTree(root.right)
        if not root.val and not root.left and not root.right:
            return None
        return root