Maximize Y‑Sum by Picking a Triplet of Distinct X‑Values

Description

You are given two integer arrays x and y, each of length n. You must choose three distinct indices i, j, and k such that:

- x[i] != x[j]

- x[j] != x[k]

- x[k] != x[i]

Your goal is to maximize the value of y[i] + y[j] + y[k] under these conditions. Return the maximum possible sum that can be obtained by choosing such a triplet of indices.

If no such triplet exists, return -1.