Problem Statement

Triangle Summation Problem Description A researcher wants a quick way to fingerprint a long numeric log so that tampering can be detected without storing the whole thing. The scheme, called 'Triangle Summation', works on a row of single digits. At each round, every pair of neighboring digits is added together, and only the ones digit (the least significant digit) of each sum is kept for the next round. Each round therefore produces a row one digit shorter than the row before it. The rounds keep repeating until exactly two digits remain, and those final two digits are the fingerprint. Given the starting row of digits, compute the fingerprint that this reduction produces, returned as a string. Examples Example 1: Input: numbers = [4, 5, 6, 7] Output: 04 Explanation: The reduction proceeds like this: Initial sequence: [4, 5, 6, 7] First step (sum adjacent digits, take least significant digit): 4 + 5 = 9 5 + 6 = 11 -> 1 6 + 7 = 13 -> 3 New sequence: [9, 1, 3] Second step: 9 + 1 = 10 -> 0 1