ElevenLabs Software Engineer Interview Experience — Three-Question OA With a Surprise 2-Minute AI Follow-up

Fresh out of the oven. 3 questions, increasing in difficulty I guess, with time limits of 25 minutes, 30 minutes and 45 minutes respectively.

Question 1: Next Number

The next_number function should return the smallest integer which is superior to n and whose digits are all different from all of n's digits.
For example, next_number(654321) return 700000.
If no such integer exists, then the function must return -1.
Write the body of the next_number(n) function.
Note: n is a strictly positive integer lower than 2^31.

Question 2: Magic Stones

You are carrying a number of stones, each having a level n expressed as an integer (0 < n < 10000).
Two stones of the same level n can be merged together to create a new stone of level n + 1.
The function magic returns the minimal number of stones that can be obtained after multiple merges.
Write the body of the function magic(stones). stones is a list of integers which contains at least one element.
For example, with [1, 2, 1], the two 1s can be merged into a 2, which then merges with the other 2 into a 3, so in the end only one stone is left and the answer is 1.

Question 3: Lowest-Cost Shirts

Suppose there is a sale on blue, green, and red shirts for the next n days. On day i, it costs bᵢ dollars to buy a blue shirt, gᵢ dollars to buy a green shirt, and rᵢ dollars to buy a red shirt.
You wish to buy a single shirt for each of the next n days, but with the caveat that you cannot buy the same color shirt on consecutive days.
Implement the function lowest_cost(blue_costs, green_costs, red_costs), which takes in three lists of length n: blue_costs, green_costs, and red_costs. Each element in these lists is a positive integer that represents the daily price of a shirt.
Your task is to output a list representing the shirt color you buy for each of the n days, such that the total combined cost of the n shirts is minimized.
Specifically, your output will be of length n, where each element in the list is either 'b', 'g', or 'r'. The ith element of the output list represents the color of the ith day's shirt.
Note that there will be exactly one color sequence that minimizes the cost for the n shirts.

Heads up, here comes the trap. After you submit, an AI generates a question asking why you did a certain step in the last problem, why you did it that way and not another way. You only get 2 minutes. You have to understand what it is asking, organize an answer, and type it out, and I didn't even finish writing mine. I think it is meant to stop candidates from using AI to generate their answers. I feel like I failed.