Delete Leaves With a Given Value

lcpy gen -n 1325   # by problem number
lcpy gen -s delete_leaves_with_a_given_value   # by problem name

Input: root = [1,2,3,2,null,2,4], target = 2
Output: [1,null,3,null,4]
Explanation: Leaf nodes in green with value (target = 2) are removed (Picture in left).
After removing, new nodes become leaf nodes with value (target = 2) (Picture in center).

Input: root = [1,3,3,3,2], target = 3
Output: [1,3,null,null,2]

Input: root = [1,2,null,2,null,2], target = 2
Output: [1]
Explanation: Leaf nodes in green with value (target = 2) are removed at each step.

from leetcode_py import TreeNode


class Solution:
    # Time: O(n) — visits each node once in post-order
    # Space: O(h) recursion stack, h = tree height
    def remove_leaf_nodes(self, root: TreeNode[int] | None, target: int) -> TreeNode[int] | None:
        if root is None:
            return None

        root.left = self.remove_leaf_nodes(root.left, target)
        root.right = self.remove_leaf_nodes(root.right, target)

        # Post-order: decide after children are pruned, so a node whose children
        # were just removed can itself qualify as a target leaf.
        if root.left is None and root.right is None and root.val == target:
            return None
        return root