Implement the sum of digits function recursively. Each call peels off one digit using modulo and integer division.
Your function takes a non-negative integer and returns the sum of its digits.
Requirements:
- Base case: single-digit number returns itself
- Recursive case:
n % 10gives last digit,n // 10gives remaining digits - Sum = last digit + sum of remaining digits
Examples:
sum_digits(123)-> ()sum_digits(5)->sum_digits(9999)->
The pattern: 123 % 10 = 3 (last digit), 123 // 10 = 12 (rest). Sum = + sum_digits().