**Objective** – Given a number, Write a program to get the sum of digits in a number till it become a single digit.

**Example**:

N = 999 -> 9+9+9 = 27-> 2+7 = 9 N = 789 -> 7+8+9= 24-> 2+4 = 6

**Approach**:

**Recursion**–

- Find the sum of all digits.
- Make a recursive call with sum calculated in step 1.
- If number is less than 10, return number.
- See the code and click on run code button for more understanding.

**Code**:

https://gist.github.com/thmain/7df55e736aaf4308d2cc4f935ec2568c

**Output**:

Sum of digits in a number 12345 till it become a single digit: 6 Sum of digits in a number 999 till it become a single digit: 9

**Tricky Approach**:

- If number is 0, return 0.
- Find remainder of number with 9. (number%9).
- If remainder is 0, return 9 else return remainder.

**Code**:

https://gist.github.com/thmain/6d3bfd19b332b13ba4eee5210184ac0c

**Output**:

Sum of digits in a number 12345 till it become a single digit: 6 Sum of digits in a number 999 till it become a single digit: 9 Sum of digits in a number 111 till it become a single digit: 3