Interview FAIL: And I thought Google was tough [closed]

Question

Okay, I've been on some hard interviews, but this was ridiculous. I was asked one question, given a pen, paper, calculator, definition of "URL-safe" characters, and 20 minutes to complete the question. The question was (as best I can remember):

Write a function to generate a unique URL-safe string that represents a given point in time for a file modification on an IIS web server that we're deploying tomorrow. The resolution of a "point in time" is one second.

.NET RegEx pattern for "URL-safe" characters = [0-9a-zA-Z\$\-\_\.\+\!\*\'\(\)]

I panicked and just wrote out my thinking instead of writing actual code. They dismissed me after viewing my "answer" because I didn't actually write any code. :(

What I wrote was something like:

- 365 days in a year so "day of year" can be represented in 2 bytes
- 4 digits in year (0 - 9999) so year can be represented in 3 bytes
- 2 digits in hour (0 - 23) so year can be represented in 1 byte
- 2 digits in minutes (0 - 59) so minutes can be represented in 1 byte
- 2 digits in seconds (0 - 50) so seconds can be represented in 1 byte

TOTAL: 2+3+1+1+1 = 8 bytes total that use 0 - 255 

- URL-safe range == 10 + 24 + 24 + 10 == 0-9 + a-z + A-Z + special chars == 68
- 4 bits required to represent URL safe char    

ANSWER:

- A byte is 8 bits
- Only 4 bits per byte needed to represented the 8 bytes in a date
- 8 / 2 = 4 

FINAL ANSWER:
- Only 4 actual bytes needed to represent hash

In other words, the timestamp hash could reasonably be represented in 4 URL-safe characters at most.

How would you have answered this?! I feel like I'm a pretty good developer but it's been many years since I've had to worry about calculating powers of two!

Answer 1

This seems almost like a FizzBuzz problem... based on requirements

DateTime.UtcNow.ToString("yyyyMMddhhmmss");

or something very similar to it is a good answer and as an interviewer I would be highly skeptical of anyone who didn't write any code because they chose to make the problem needlessly complicated.