Harshad Number

Problem Description

An integer divisible by the sum of its digits is said to be a Harshad number. You are given an integer x. Return the sum of the digits of x if x is a Harshad number, otherwise, return -1.

Key Insights

• A Harshad number is an integer that is divisible by the sum of its digits.
• To determine if a number is a Harshad number, we need to:
  • Calculate the sum of its digits.
  • Check if the original number is divisible by this sum.
• The constraints (1 <= x <= 100) allow for a straightforward implementation without performance concerns.

Space and Time Complexity

Time Complexity: O(d), where d is the number of digits in x (at most 3 for the constraint given). Space Complexity: O(1), as we are using a constant amount of space.

Solution

To solve the problem, we can use a simple approach:

1. Convert the number into its individual digits.
2. Calculate the sum of these digits.
3. Check if the original number is divisible by this sum.
4. Return the sum if it's a Harshad number, otherwise return -1.

The data structure used here is just integers, and the algorithm is a straightforward arithmetic and control flow.

Code Solutions