Finding the group with largest elements with same digit sum in JavaScript

We are required to write a JavaScript function that takes in a positive integer, say n, as the only argument.

The function should first group the integers from 1 to n to subarray where a specific subarray contains all the elements contains a specific digit sum. Then the function should examine each subarray and return the length of that subarray which contains the most elements.

For example −

If the input number is −

const num = 15;

Then the output should be −

const output = 2;

because the groups are −

[1, 10], [2, 11], [3, 12], [4, 13], [5, 14], [6, 15], [7], [8], [9]

Example

Following is the code −

const num = 67;
const countLargestGroup = (num = 1) => {
   if(num < 10){
      return num;
   };
   let res = 0;
   let temp = 0;
   let map = {};
   for(let i = 1; i <= num; i++){
      let sum = 0;
      let num = i;
      while (num) {
         sum += num % 10;
         num = Math.floor(num / 10);
      }
      if(map[sum] != undefined){
         map[sum]++;
      } else {
         map[sum] = 1;
      }
   };
   for (const key of Object.keys(map)) {
      if(temp == map[key]){
         res++;
      }
      else if(temp < map[key]){
         res = 1;
         temp = map[key];
      }
   };
   return res;
};
console.log(countLargestGroup(num));

Output

Following is the console output −

4