Digit Sum Sorting

Problem: Digit Sum Sorting

Write a function that takes an array of integers and returns a new array where the numbers are sorted based on the following rules:

1. Primary sort key: Sum of the digits of the number (in ascending order).
2. Secondary sort key: The numerical value itself (in ascending order) if two numbers have the same digit sum.

Example

For the input: [56, 65, 74, 100, 99, 68, 86, 180, 90]

• Digit sums:
  • 56 -> 5 + 6 = 11
  • 65 -> 5 + 6 = 11
  • 74 -> 7 + 4 = 11
  • 100 -> 1 + 0 + 0 = 1
  • 99 -> 9 + 9 = 18
  • 68 -> 6 + 8 = 14
  • 86 -> 8 + 6 = 14
  • 180 -> 1 + 8 + 0 = 9
  • 90 -> 9 + 0 = 9

Sorting based on the rules gives the output:

[100, 90, 180, 56, 65, 74, 68, 86, 99]

Notes

• Assume the input array contains at least one integer.
• Consider edge cases such as single-digit numbers and numbers with the same digit sum.

This problem is inspired by sorting methodologies and is a good exercise for developing custom sort comparators.

Happy coding!