Triangular Sum TikTok Python Interview Question

You are given an integer array , where each element in it is a single digit (0-9).

The triangular sum of is the value of the only element present in nums after the following process terminates:

1. Let comprise of elements. If , end the process. Otherwise, create a new integer array of length .
2. For each index , assign the value of as , where denotes the modulo operator.
3. Replace the array with .
4. Repeat the entire process starting from step 1.

Return the triangular sum of nums.

Test Case #1:

Input: nums =

1. Iteration #1: Form = [(1 + 3) % 10, (3 + 5) % 10, (5 + 7) % 10] = [4, 8, 2].

2. Iteration #2: Form = [(4 + 8) % 10, (8 + 2) % 10] = [2, 0].

3. Iteration #3: Form = [(2 + 0) % 10] = [2].

The triangular sum of is 2.

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Test Case #2:

Input: nums =

1. Iteration #1: Form = [(9 + 7) % 10, (7 + 5) % 10, (5 + 3) % 10] = [6, 2, 8].

2. Iteration #2: Form = [(6 + 2) % 10, (2 + 8) % 10] = [8, 0].

3. Iteration #3: Form = [(8 + 0) % 10] = [8].

The triangular sum of is 8.

Brute force(simulation)

This is the type of question where you will just do what the problem statement says. We will just follow the rules until we are left with an array with only one number.

Here is the code:

Recursive approach

Since there isn't much optimization to do, the interviewer might ask you to solve the problem using multiple approaches during an interview. One other way of solving this problem is through recursion.

Base Case:

In recursion, the base case is the simplest version of the problem where the recursion stops. For this problem, the base case occurs when we are left with just one number in the list. This is the final triangular sum, so we simply return it.

Recursive Case:

The recursive case is where the problem is broken down into smaller subproblems. Here’s what we do in each recursive step:

1. Create a new list () where each element is the sum of two consecutive elements from the original list, modulo 10.
2. Recursively call the function on this smaller list () until we hit the base case.

Here is the full recursive solution: