Check if given number is armstrong in javascript

An algorithm to check if given number is Armstrong number in Javascript.

We will check if the given number is Armstrong number in Javascript and return true or false accordingly.

Example

Input:
153    // 1 * 1 * 1 +  5 * 5 * 5 + 3 * 3 * 3 = 1 + 125 + 27 = 153
127    // 1 * 1 * 1 +  2 * 2 * 2 + 7 * 7 * 7 = 1 + 8 + 343 = 352

Output:
true
false

Implementation

• We are going to extract each digit of the given number and cube it.
• Then we will add all the cubes and check if it is equal to the given number.
• Everything will be written in ES6.

let isArmstrong = (num) => {
  let sum = 0;
  //store the actual number to check later
  let temp = num;

  //Extract each digit of number
  while(num > 0){
    //get the last digit of the number
    let d = parseInt(num % 10);
  
    //find the cube
    d = d ** 3;
    sum = sum + d;
  
    //reduce the number
    num = parseInt(num / 10);
  }
  
  //Check if number equals to the cubed sum
  return temp === sum;
}

Input:
console.log(isArmstrong(407));
console.log(isArmstrong(370));
console.log(isArmstrong(371));
console.log(isArmstrong(153));
console.log(isArmstrong(154));
console.log(isArmstrong(152514214));

Output:
true
true
true
true
false
false

Time complexity: O(logn) or O(d).

Space complexity: O(1).

Time and Space complexity

• We are extracting each digit from the number, so Time complexity is O(logn) or O(d) where d is the no of digits.
• We are using constant space, so Space complexity is O(1).