Given an integer array nums, choose two distinct indices i and j such that the sum of digits of nums[i] is equal to the sum of digits of nums[j]. Among all such valid pairs, return the maximum possible value of nums[i] + nums[j]. If no valid pair exists, return -1.

Constraints:

• $1 \leq$ nums.length $\leq 10^5$

• $1 \leq$ nums[i] $\leq 10^9$

Input: nums = [51, 42, 33, 24, 15]-List[int]
Output: 93-int
Explanation: The digit sums are 51→6, 42→6, 33→6, 24→6, and 15→6, so any two numbers form a valid pair, and the maximum sum comes from 51 + 42 = 93.

Input: nums = [8, 17, 26, 35, 44]-List[int]
Output: 79-int
Explanation: The digit sums are 8→8, 17→8, 26→8, 35→8, and 44→8. All share the same digit sum, so we choose the two largest values: 44 + 35 = 79.

Input: nums = [999999999, 100000000, 90909090, 123456789]-List[int]
Output: -1-int
Explanation: The digit sums are 999999999→81, 100000000→1, 90909090→36, and 123456789→45. No digit sum appears at least twice, so no valid pair exists.

Input: nums = [1, 2, 3, 4, 5, 6]-List[int]
Output: -1-int
Explanation: The digit sums are the numbers themselves (all distinct), so there is no pair with equal digit sum.

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