I applied on the careers page for a Software Engineer Internship and was contacted by a recruiter three months later. I was then scheduled for a video screening interview that involved two technical questions:

1. Check for a palindrome in a string, ignoring special characters. Example: "&^ab*ab" is a palindrome in O(N) time and O(1) space.
2. Validate if a Binary Tree is a Binary Search Tree in O(N) time and O(1) space.

After that, I was scheduled for a video onsite interview:

1. Determine whether an array contains a contiguous sub-array whose elements sum up to a given number in O(N) time and O(1) space.

The interviewer didn't seem very interested in interviewing me and appeared to be in a hurry.

I solved the final interview question optimally, but I didn't know the solution from the start. I had to develop the algorithm myself during the interview, which took some time. Getting to the solution involved changing my initial approach. I received a rejection call two business days later. The reasons given were:

• I didn't clarify the new approach when my original approach didn't work and started coding immediately. I recall stating that the original approach wouldn't work and needed changes, rather than just continuing. I also had no clear idea of the new approach I was going to implement and explained my thoughts as I developed the solution, instead of explaining it all upfront. I'm unsure how I could have clarified my approach differently, as I could only explain that it needed changes and wouldn't work as initially conceived, which I did.
• The approach seemed overly complicated to the interviewer. I was considering adding more elements to the solution to make it more efficient when he asked if it needed anything else (but I didn't add anything when he pointed out it wasn't required). This was termed needless and considered "complicated."
• I didn't test any test cases other than the ones provided. However, I also didn't test other cases in the first interview. Therefore, I don't understand why this was expected in the onsite interview, as the recruiter stated it would follow the same format.

Overall, this rejection didn't seem fair to me, and I was not satisfied with the outcome.

Check whether a string is a palindrome or not, ignoring special characters. For example, "&^ab*ab" is a palindrome.

Validate a Binary Tree for being a Binary Search Tree in O(N) time and O(1) space.

Determine whether an array contains a contiguous sub-array whose elements sum up to a given number in O(N) time and O(1) space.