I met Uber at the CS career fair/university recruiting event, and they set up a one-hour interview on campus.

It was just one engineer in a small room with a whiteboard, and he was really nice! Even though the question was pretty hard, it was fun because the interviewer was nice. It wasn't what I expected from Uber, haha.

Given an input string of numbers, like '121', find all permutations of that number. The permutations should correspond to the letters for each number. For example, '121' can be broken down into:

• 1 2 1
• 12 1
• 1 21

These correspond to letter combinations like ABA, LA, and AT.