2221. Find Triangular Sum of an Array

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. If n == 1, end the process. Otherwise, create a new 0-indexed integer array newNums of length n - 1.

• For each index i, where 0 <= i <&nbsp;n - 1, assign the value of newNums[i] as (nums[i] + nums[i+1]) % 10, where % denotes modulo operator.

• Replace the array nums with newNums.

• Repeat the entire process starting from step 1.

Return the triangular sum of nums.

  Example 1:

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.

Example 2:

Input: nums = [5]
Output: 5
Explanation:
Since there is only one element in nums, the triangular sum is the value of that element itself.

  Constraints:

• 1 <= nums.length <= 1000

• 0 <= nums[i] <= 9

Solution (Java)

class Solution {
    public int triangularSum(int[] nums) {
        int len = nums.length;
        while (len-- > 1) {
            for (int i = 0; i < len; i++) {
                nums[i] += nums[i + 1];
                nums[i] %= 10;
            }
        }
        return nums[0];
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).