4 ms·

If and when people ask me this (exact) question I like to tell them that although I can implement the O(1) solution, I just copied it off of a 14 year old.

• rietta 11y ago
  Seperates those who remember their math from those who don't! Brilliant. I love the Gauss equation for this (had to look it up, I need to review math more).
• talideon 11y ago
  A totally acceptable answer. :-)