dongido001 / hackerank-super-digit

Recursive Digit Sum

hackerank's Super Digit Solution (Recursive Digit Sum)

Problem Definition

find the problem on hackrank.

We define super digit of an integer x using the following rules:

Given an integer, we need to find the super digit of the integer.

• If x has only 1 digit, then its super digit is x.

• Otherwise, the super digit of x is equal to the super digit of the sum of the digits of x.

For example, the super digit of 9875 will be calculated as:

	super_digit(9875)   	9+8+7+5 = 29 
	super_digit(29) 	2 + 9 = 11
	super_digit(11)		1 + 1 = 2
	super_digit(2)		= 2  

Example

 n='9875' 
 
 k=4

The number p is created by concatenating the string n k times so the initial p = 9875987598759875.

superDigit(p) = superDigit(9875987598759875)
                  9+8+7+5+9+8+7+5+9+8+7+5+9+8+7+5 = 116
    superDigit(p) = superDigit(116)
                  1+1+6 = 8
    superDigit(p) = superDigit(8)

All of the digits of p sum to 116. The digits of 116 sum to 8. 8 is only one digit, so it is the super digit.

My Solution

solution.js