var lowestCommonAncestor = function (root, p, q) {
  if (!root) return null;
  let res = null;
  const rec = (root) => {
    if (root.val > p.val && root.val > q.val) {
      root.left && rec(root.left);
    } else if (root.val < p.val && root.val < q.val) {
      root.right && rec(root.right);
    } else {
      res = root;
    }
  };
  rec(root);
  return res;
};