Armstrong Number in JavaScript

An Armstrong number is a special integer in which the sum of its digits, raised to the power of the number's length, is equal to the number. For instance, 153 is an Armstrong number since 1^3 + 5^3 + 3^3 = 153.

Definition of Armstrong Number

An Armstrong number is a number in which the sum of cubes of its digits is equal to the number itself. It can also be described as a narcissistic number. A number will be called a narcissistic number or an Armstrong number if the sum of n-th powers of its digits (where n represents the number of digits) equals the number.

We can identify whether a provided number is an Armstrong number with the help of a simple JavaScript program. The program will take an integer as input and let us know whether the number is an Armstrong number or not. The subsequent parts will describe how to create such a program in JavaScript.

The Logic of Armstrong Number in JavaScript

In the JavaScript code to test whether a number is an Armstrong number, we will accept an integer. Following the definition of an Armstrong number given above, if the given number has n digits, then it is an Armstrong number when the sum of every digit taken to the nth power is the same as the original number. Thus, the logic to find an Armstrong number will be:

We will pull all the digits from the input number using JavaScript loops. We will then take the nth power of each digit pulled and sum them up. If the summed value is the same as the original number put in, the number is an Armstrong number. If the value is not equal to the number entered, the number is not an Armstrong number. As far as time complexity is concerned, checking if an integer 'n' is an Armstrong number takes O(log(n)) time complexity.

The flow chart for the JavaScript program that checks if a number is an Armstrong number is given below.

An example of a three-digit number is 153:

Thus, 153 is classified as an Armstrong number.

Now consider

Because this is not equal to the original number, 123 is not an Armstrong number. Only four three-digit Armstrong numbers exist. For all other powers, the value of n will differ. For a four-digit number, the power will be 4.

For example, 1634 can be calculated as follows:

Here, as we have 4 digits, we have used 4 as power.

Examples of Armstrong Numbers in JavaScript

Here are some examples of Armstrong numbers implemented in JavaScript:

Example 1: Using a while loop

Code

In this section, we generalized the formula for finding an Armstrong number. First, we find the number of digits of the number input by the user and use that to decide the power required for calculation. We use a while loop to read each digit of the number one by one and then carry out the required processing.

Output

For a valid Armstrong number:

For an Invalid Armstrong number:

Example 2: Using for loop

We can also iterate using a for loop to find the sum. The strategy for finding the Armstrong number will remain the same in both cases. This is just for demonstration purposes of another JavaScript implementation.

Code

We have employed a for loop to find the sum in this example. We can keep going through each of the digits until we are done with all of them.

Output

For a valid Armstrong number:

For an invalid Armstrong number:

Conclusion

1. A n-digit number is an Armstrong number if the sum of the n-th powers of its digits is equal to the number.
2. You can figure out whether a number is an Armstrong number or not by using a simple JavaScript program.
3. The time complexity for checking if an integer 'n' is an Armstrong number is O(log(n)).