Next Number with Distinct Digits CCC 2013 Senior 1

Question

The 2013 CCC Senior 1 problem on page 4 is to find the smallest number that is larger than the input with distinct digits as the title explains. I'm a total beginner at programming and I can't find what's wrong with this code:

year = 1987
distinct = 'no'
a = []
while distinct != 'yes':
    year += 1
    for i in str(year):
        if i not in a:
            a.append(i)
            distinct = "yes"
        else:
            distinct = "no"
            break

print(year)

I think the code is still in the while loop but I don't understand why. The code above is supposed to print 2013. Thank you for your help.

Answer 1

Your approach to increment the year by 1 and check if the digits are distinct is correct, and your code is almost correct. Your mistake is that you initialize a[] , your set of digits in the year, only once, but it should be initialized to empty for each year. Move the line a = [] to after the line year += 1 and give it the proper indentation and your code will work. That would make your code into:

year = 1987
distinct = 'no'
while distinct != 'yes':
    year += 1
    a = []
    for i in str(year):
        if i not in a:
            a.append(i)
            distinct = "yes"
        else:
            distinct = "no"
            break

print(year)

Another approach is to use a set, which automatically removes any duplicates. You can check if making the string of the year into a set changes its size. So perhaps use this, which also avoids using a status variable like distinct :

year = 1987
year += 1
while len(set(str(year))) != len(str(year)):
    year += 1
print(year)

If you want that status variable, or do not like that repeated line year += 1 , you could do this:

year = 1987
distinct = False
while not distinct:
    year += 1
    if len(set(str(year))) == len(str(year)):
        distinct = True
print(year)