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The iterative approach involves summing the digits of the number repeatedly until the sum becomes a single-digit number. This is a straightforward approach and uses basic loops to repeatedly process the digits of the number.
1using System;
2
3public class AddDigitsIterative {
4 public static int AddDigits(int num) {
5 while (num >= 10) {
6 int sum = 0;
7 while (num > 0) {
8 sum += num % 10;
9 num /= 10;
10 }
11 num = sum;
12 }
13 return num;
14 }
15
16 public static void Main() {
17 int num = 38;
18 Console.WriteLine(AddDigits(num));
19 }
20}The approach in C# employs nested loops to repeatedly add the digits until the number is reduced to a single digit.
The mathematical approach leverages a known number theory result related to digit root which can be deduced using modulo 9 arithmetic. The result for the repeated digit sum is equivalent to the number modulo 9, except that when the number is zero it should remain zero.
1function
JavaScript similarly computes the result using direct arithmetic manipulation, ensuring optimal performance.