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import { TreeNode } from "../mod.ts";
export default function pruneTree(root: TreeNode | null): TreeNode | null {    if (!root) return null;    const left = pruneTree(root.left);    const right = pruneTree(root.right);    if (root.val === 0 && !left && !right) return null;
    return new TreeNode(root.val, left, right);}