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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.
1function addDigits(num) {
2 while (num >= 10) {
3 let sum = 0;
4 while (num > 0) {
5 sum += num % 10;
6 num = Math.floor(num / 10);
7 }
8 num = sum;
9 }
10 return num;
11}
12
13console.log(addDigits(38));The JavaScript solution also relies on loops to process and sum the digits until a single digit is left.
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.
1#include
This C solution uses modulo 9 to calculate the digit root. This gives us a constant time solution which is highly efficient.