Meta Software Engineer - Intern interview questions

Write a function to determine if a string is a palindrome.

Write a function to determine if a bin tree is a valid BST. I wrote a fully working solution in 3-5 minutes. It was also the most optimal but maybe because she needed to kill time, she asked me to rewrite it in what she thought was optimal (her reasoning didn't make much sense). Then she asked me for time and space requirements of the solutions. I said O(n) for both which is correct but she insisted that the space requirement was O(logn) which is wrong.