Problem 3069. Pattern Recognition 2 - Known Unit Length, Various Array Length (including cell arrays)

You will be given various arrays, composed of numbers or strings, including cell arrays of strings. For this problem, the known pattern unit length is three. Write a function to determine if the supplied array is a strict repeating pattern. The array will not necessarily have a length that is a multiple of three.

For example, [1 2 3 1 2 3 1 2 3 1] would return true since the first block ([1 2 3]) is strictly repeated through the remainder of the array (including the last 1). On the other hand, [1 2 3 3 2 3 1 2 3] would return false, since the second block is [3 2 3] rather than [1 2 3], as indicated by the first block.

This problem is a follow-on to Problem 3068 and a precursor to Problem 3070.