Leetcode 3201. Find the Maximum Length of Valid Subsequence I

Find the maximum-length subsequence whose adjacent sums all have the same parity — equivalently either all elements have the same parity or the subsequence strictly alternates parity. The challenge is to compute, while preserving order, the longest same-parity subsequence (all odds or all evens) or the longest parity-alternating subsequence and return the larger length.