mycsmajor
Python problem 3 of 30

Sum of the digits

  • Python
  • Easy

Write digit_sum(n) that returns the sum of the digits of the integer n. Negative numbers should work too.

digit_sum(4096)   # 19
digit_sum(-25)    # 7
digit_sum(0)      # 0
Show hint

n % 10 is the last digit of n, and n // 10 drops it.

Show solution 
def digit_sum(n):
    n = abs(n)
    total = 0
    while n > 0:
        total += n % 10
        n //= 10
    return total

Each loop peels off the last digit with % 10 and removes it with // 10. abs handles negatives. The one-line version is sum(int(d) for d in str(abs(n))), which is fine too. Both are O(number of digits).

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