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6 kyu · algorithms

Sum of Digits / Digital Root

MathematicsAlgorithms

Digital root is the recursive sum of all the digits in a number.

Given n, take the sum of the digits of n. If that value has more than one digit, continue reducing in this way until a single-digit number is produced. The input will be a non-negative integer.

Examples

    16  -->  1 + 6 = 7
   942  -->  9 + 4 + 2 = 15  -->  1 + 5 = 6
132189  -->  1 + 3 + 2 + 1 + 8 + 9 = 24  -->  2 + 4 = 6
493193  -->  4 + 9 + 3 + 1 + 9 + 3 = 29  -->  2 + 9 = 11  -->  1 + 1 = 2

Solutions

01-solution.jsView on GitHub ↗
function digital_root(n) {
  const str = `${n}`;
  const nbr = str.split("").map(Number).reduce((c, i) => {
    r = c + i;
    while(`${r}`.length > 1) {
      c += digital_root(r);
    } 
      c = r;
    
    return c;
  }, 0);

  return nbr;
}