Find Triangular Sum of an Array — LeetCode 2221 Python Solution

The problem

You are given a 0-indexed integer array nums, where nums[i] is a digit between 0 and 9 (inclusive). The triangular sum of nums is the value of the only element present in nums after the following process terminates: Let nums comprise of n elements.

Example

Input

nums = [1,2,3,4,5]

Output

8

Explanation

The above diagram depicts the process from which we obtain the triangular sum of the array.

Python solution

class Solution:
    def triangularSum(self, nums: List[int]) -> int:
        for k in range(len(nums) - 1, 0, -1):
            for i in range(k):
                nums[i] = (nums[i] + nums[i + 1]) % 10
        return nums[0]

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 2221. Find Triangular Sum of an Array is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math and Combinatorics.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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