Question

Write a function (method) that takes as input a large number and returns a single digit by
performing continuous digitSum on this number, and on the resulting numbers, till the resulting
number is a single digit number in the range 1 to 9.
Example 1: If the large number whose single-digit digitSum is to be found is 976592, the process is
as below
9+7+6+5+9+2 = 38
3+8 = 11
1+1=2
Thus, the single-digit digitSum for the number 976592 is 2.
Example 2: If the large number whose single-digit digitSum is to be found is 123456, the process is
as below -
1+2+3+4+5+6 = 21
2+1 = 3
Thus, the single-digit digitSum for the number 123456 is 3.
​

Answer 1

digitSum: The labels on a trader's boxes display a large number (integer). The trader wants to label the boxes with a single digit ranging from 1 to 9. He decides to perform digit sum on this large number, continuously till he gets a single digit number.

NOTE: In mathematics, the "digit sum" of a given integer is the sum of all its digits, (e.g.: the digit sum of 84001 is calculated as 8+4+0+0+1 = 13, the digit sum of 13 is 1+3 = 4).

Write a function (method) that takes as input a large number and returns a single digit by performing continuous digitSum on this number, and on the resulting numbers, till the resulting number is a single digit number in the range 1 to 9.

Example 1: If the large number whose single-digit digitSum is to be found is 976592, the process is as below –

9+7+6+5+9+2 = 38

3+8 = 11

1+1 = 2

Thus, the single-digit digitSum for the number 976592 is 2.

Example 2: If the large number whose single-digit digitSum is to be found is 123456, the process is as below –

1+2+3+4+5+6 = 21

2+1 = 3

Thus, the single-digit digitSum for the number 123456 is 3.

For negative numbers, the result should also be in negative.

Example 3: If the large number whose single-digit digitSum is to be found is -123456, the answer would be -3.