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import { TreeNode } from "../mod.ts";
function isUnivalTree(root: TreeNode | null): boolean {    if (!root) return true;    return dfs(root, root.val);}function dfs(root: TreeNode | null, val: number): boolean {    if (!root) return true;    return root.val === val && dfs(root.left, val) && dfs(root.right, val);}export default isUnivalTree;