DSA problem

Sum of Digits of a Number

EasyMathPattern: MathbeginnerFree

Given an integer N, compute the sum of its digits.

This is the simplest application of digit extraction: take the last digit with N % 10, add it to a running total, then drop it with integer division, repeating until N reaches 0. Take the absolute value first so negative inputs are handled correctly.

Digit sums power real algorithms: repeatedly summing digits gives a digital root, used in check-digit schemes like Luhn's algorithm (credit-card validation) and ISBN validation. A neat fact - the digital root of any multiple of 9 is always 9 - connects digit sums to modular arithmetic.

Examples

Constraints

• -10^9 <= N <= 10^9

3 hints and a full solution walkthrough with step-by-step visualizations are available in the practice editor.

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