We meet again. Our second question in the study plan is the question on how to compute the n-th tribonacci (a pun off of “fibonacci”) number. Again I am not sure if we should really use this to teach dynamic programming! We’re just practicing the array tables.

In truth I don’t have much to say. This definitely is able to be done after solving the first question. I am a fan of these sort of “very basic extensions” to previous questions to help the student drive home the idea. I just went with the table approach this time.

I suppose it’s interesting that the question is articulated slightly differently in the codewars question. There is something a bit more general there; I prefer the specificity if I were using this question in a classroom or review setting. Maybe as a side-note, or a “quick” homework question, would be to further extend to these sort of signatures.

Anyways, here’s the solution:

class Solution:
    def tribonacci(self, n: int) -> int:
        a = [0, 1, 1]
        if n < 3: return a[n]
        for i in range(3, n+1):
            a.append(a[i-3]+a[i-2]+a[i-1])
        return a[-1]