Digit root of some positive integer is defined as the sum of all of its digits. We are given an array of integers. We have to sort it in such a way that if a comes before b if the digit root of a is less than or equal to the digit root of b. If two numbers have the same digit root, the smaller one (in the regular sense) should come first. For example, 4 and 13 have the same digit root, however 4 < 13 thus 4 comes before 13 in any digitRoot sorting where both are present.
For Example,
for a = [13, 20, 7, 4], the output should be [20, 4, 13, 7].
Let’s write the code for this problem −
We will divide it in two functions, a recursive function that counts the sum of digits of a number, and then a sorting function that orders the element on the basis of the sum of digits.
The code for this will be −
Example
const arr = [54, 23, 8, 89, 26];
const recursiveCount = (num, count = 0) => {
if(num){
return recursiveCount(Math.floor(num/10), count+num%10);
};
return count;
};
const sorter = (a, b) => {
const countDifference = recursiveCount(a) - recursiveCount(b);
return countDifference || a - b;
};
arr.sort(sorter);
console.log(arr);Output
The output in the console will be −
[ 23, 8, 26, 54, 89 ]