Check whether an user given number is a magic number or not

Question

To me:

Magic Number: If sum of digits of a number becomes 1 until length of resultant becomes 1 is called magic number.

example: 1 [ sum: 1], 10 [sum: 1 + 0 = 1], 91 [sum: pass1: 9 + 1 = 10, pass2: 1 + 0 = 1], 100 [sum: 1 + 0 + 0 = 1] like these.

Problem is: My code is working fine for input: 91, sum of digits of 91 is: pass1: 9 + 1 = 10, pass2: 1 + 0 = 1. It is showing correct output. But not working for any other input like: 100, 55 etc.

Code:

def Single_Digit_Summer(num):
    sum = 0
    while num > 0:
        sum += num % 10
        num = num // 10
    return Single_Digit_Summer(sum) if sum > 9 else sum
num15 = int(input("Enter number to check: "))
sum2 = Single_Digit_Summer(num15)
print(num15, "is a magic number.") if sum2 == 1 else print(num15, "is not a magic number.")

Output:

Case - 1:

Terminal: Enter number to check: 
Terminal input:91
Terminal output: 91 is a magic number.
Actual var 'sum' value: 1
Expected var 'sum' value: 1
Expected output: 91 is a magic number.
Decision: OK

Case - 2:

Terminal: Enter number to check: 
Terminal input:100
Terminal output: 100 is not a magic number.
Actual var 'sum' value: 0
Expected var 'sum' value: 1
Expected output: 100 is a magic number.
Decision: Wrong Output

Case - 3:

Terminal: Enter number to check:
Terminal input:55
Terminal output: 55 is not a magic number.
Actual var 'sum' value: 5
Expected var 'sum' value: 1
Expected output: 55 is a magic number.
Decision: Wrong Output

Case - 4:

Terminal: Enter number to check:
Terminal input: 1009
Terminal output: 1009 is not a magic number.
Actual var 'sum' value: 9
Expected var 'sum' value: 1
Expected output: 1009 is a magic number.
Decision: Wrong Output

Requirement: I can't find why my code is not working. help me debugging.

Just add some debug output, that helps in 99% of cases. A simple `print(sum, num)` inside the loop will do the job. — IcedLance, Jul 10 '19 at 06:09
I am getting different output that you are reporting: `55 is a magic number.` & `100 is a magic number.` — Mark, Jul 10 '19 at 06:17

score 0 · Answer 1 · answered Apr 07 '22 at 06:51

This can be solved using simple observation. If you know divisibility rule of 9, which tales that a number is divisible by 9 if the sum of digits is multiple of 9. In your case you need to check end digit sum 1, which depicts that if you divide number by 9 and remainder is 1, then its magic number. Hence, it can be written as:

def Single_Digit_Summer(num):
    if(num%9 ==1):
       return 1
    return 0

Check whether an user given number is a magic number or not

1 Answers1