Uber Software Engineer New Grad interview questions

In the HR round, questions like, "What made you apply?", "Why Uber?" In the first tech round, asked a binary tree question - skew it all to the right (as in unbalance it). I was able to come up with a brute force solution, told the interviewer but he asked me to come up with a O(1) space solution. I think I did well, was able to code the solution, but was not able to correctly explain the solution - I think that's where it went awry. :(