coderbyte-hard-KaprekarsConstant.py

'''
Challenge(hard)

Have the function KaprekarsConstant(num) take the num parameter being passed which will be a 4-digit number with at least two distinct digits. Your program should perform the following routine on the number: Arrange the digits in descending order and in ascending order (adding zeroes to fit it to a 4-digit number), and subtract the smaller number from the bigger number. Then repeat the previous step. Performing this routine will always cause you to reach a fixed number: 6174. Then performing the routine on 6174 will always give you 6174 (7641 - 1467 = 6174). Your program should return the number of times this routine must be performed until 6174 is reached. For example: if num is 3524 your program should return 3 because of the following steps: (1) 5432 - 2345 = 3087, (2) 8730 - 0378 = 8352, (3) 8532 - 2358 = 6174. 

Hard challenges are worth 15 points and you are not timed for them.
Sample Test Cases

Input:2111

Output:5


Input:9831

Output:7

'''

count = 0

def KaprekarsConstant(num): 
    global count
    if num == '6174':
        return count
    else:
        num1 = "".join(sorted(str(num))) #ascending order
        num2 = "".join(sorted(str(num), reverse=True)) #descending order
        num1 = int(num1)
        num2 = int(num2)
        subtractResult = abs(num1 - num2)
        diff = str(subtractResult)
        diffLength = len(diff)
        if diffLength < 4:
            for i in range(0, 4-diffLength):
                diff = '0' + diff
        count += 1
        return KaprekarsConstant(str(diff))
    
# keep this function call here  
print KaprekarsConstant(raw_input())