Top of the Digit Pyramid

Medium

The bottom row of a pyramid holds the digits from the list digits. Each row above is one cell shorter: the cell sitting on two neighbours gets the last digit of their sum, that is (a + b) % 10. Rows keep being built until a single cell is left. Return the digit at the top of the pyramid.

Example 1

digits=[3, 8, 6] → 5

The second row is (3 + 8) % 10 = 1 and (8 + 6) % 10 = 4. The top is (1 + 4) % 10 = 5.

Example 2

digits=[9, 9, 9, 9] → 2

The rows go [8, 8, 8], then [6, 6], then [2], so the top is 2.

Example 3

digits=[7] → 7

A single digit is already the top.

Constraints

1 ≤ len(digits) ≤ 1000
0 ≤ digits[i] ≤ 9

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Topics

Array Math Combinatorics Simulation

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Input

digits=[3, 8, 6]

Expected

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