Finding Out the Harshad Number in JavaScript

Harshad numbers are those numbers which are exactly divisible by the sum of their digits. Like the number 126, it is completely divisible by 1+2+6 = 9.

• All single digit numbers are harshad numbers.

• Harshad numbers often exist in consecutive clusters like [1,2,3,4,5,6,7,8,9,10], [110,111,112], [1010, 1011, 1012].

Our job is to write a function that takes in a Number as input checks whether it’s a harshad number or not, if not then returns -1 otherwise it returns the length of streak of consecutive harshad cluster.

For example −

harshadNum(1014) = harshadNum(1015) = harshadNum(1016) = harshadNum(1017) = 4
harshadNum(1) = 10
harshadNum(12) = 1
harshadNum(23) = -1

Let’s break this problem into two major functions,

• isHarshad() →  takes in a number num and returns a boolean depending upon whether the number is harshad or not.

• harshadNum() → main function that takes in the actual number, makes call to isHarshad() at various points and returns the length of streak.

Coding the isHarshad function() −

const isHarshad = (num) => {
   let sum = 0, temp = num;
   while(temp){
      sum += temp % 10;
      temp = Math.floor(temp/10);
   }
   return num % sum === 0;
}

Pretty simple iterative function that returns a boolean

Now let’s code the harshadNum() function −

const harshadNum = (number) => {
   //if the input is not harshad return -1
   if(!isHarshad(number)){
      return -1;
   }
   let streak = 1, prev = number-1, next = number+1;
   //check preceding streak
   while(isHarshad(prev) && prev > 0){
      streak++;
      prev--;
   }
   //check succeeding streak
   while(isHarshad(next)){
      streak++;
      next++;
   }
   return streak;
};
console.log(harshadNum(1014));

Understanding the above code −

• Check whether the input is harshad or not, if not stop the function and return -1;

• Run one loop backwards, one forwards while we keep getting harshad numbers,simultaneously keep updating the streak

• Lastly return the streak

Following is the complete code −

Example

const isHarshad = (num) => {
   let sum = 0, temp = num;
   while(temp){
      sum += temp % 10;
      temp = Math.floor(temp/10);
   }
   return num % sum === 0;
}
const harshadNum = (number) => {
   //if the input is not harshad return -1
   if(!isHarshad(number)){
      return -1;
   }
   let streak = 1, prev = number-1, next = number+1;
   //check preceding streak
   while(isHarshad(prev) && prev > 0){
      streak++;
      prev--;
   }
   //check succeeding streak
   while(isHarshad(next)){
      streak++;
      next++;
   }
   return streak;
};
console.log(harshadNum(1014));

Output

Output for this code in the console will be −

4