Count Four-Digit Combinations with Given Digit Sum

google Given an integer 'sum', find all combinations of four digits (0-9) that sum to 'sum'. Calculate the total number of such combinations. The input is an integer 'sum'. The output is the number of all valid combinations. Example: Input: 12 Output: 15 Explanation: There are 15 combinations such as 0039, 0138, ..., 4440 that sum to 12. Example Input 0