Max Sum of Pair in RUBY!
IntuitionThe key observation is that we need to find pairs of numbers with the same sum of digits. My initial thought was to calculate the sum of digits for eac
# Intuition
The key observation is that we need to find pairs of numbers with the same sum of digits. My initial thought was to calculate the sum of digits for each number and then group numbers with the same sum together. Once grouped, we can find the maximum sum of any two numbers within each group.

# Approach
1. Create a helper function to calculate the sum of digits of a given number.
2. Use a hash map to group numbers by their sum of digits.
3. Iterate through the input array, calculate the sum of digits for each number, and add it to appropriate group in the hash map.
4. After grouping, iterate through each group in the hash map.
5. For each group with at least two numbers, sort the numbers in order and find the sum of the two numbers.
6. Keep track of the maximum sum found across all groups.
. If no valid pair is found (i.e., no group has at least two numbers), return -1.

# Complexity
 Time complexity:
The time complexity is O(n log n), where n is the length of the input array. This is due to the sorting step within each group. In the worst case, all numbers might fall into a group, leading to sorting all n numbers.

- Space complexity:
The space complexity is O(n) to store the hash map, which in the worst case could contain all n numbers from the input array.

# Code
```ruby
# @param {Integer[]} nums
# @return {Integer}
def maximum_sum(nums)
  # Function to calculate the sum of digits of a number
  def sum_of_digits(num)
    num.to_s.chars.map(&:to_i).sum
  end

  # Hash map to store numbers grouped by their sum of digits
  digit_sum_map = Hash.new { |h, k| h[k] = [] }

  # Group numbers by their sum of digits
  nums.each do |num|
    digit_sum = sum_of_digits(num)
    digit_sum_map[digit_sum] << num
  end

  max_sum = -1

  # Find the maximum sum of any two numbers with the same sum of digits
  digit_sum_map.each_value do |numbers|
    next if numbers.size < 2
    numbers.sort!.!
    max_sum = [max_sum, numbers[0] + numbers[1]].max
  end

 _sum
end
```
['Ruby']