I’m coding in python and I want to change the mapping of my characters so that if the same character is printed again the value of it changes to 1 and another value takes the value of the initial place.

My code so far is:

def custom_mapping(hex_string):
    # Define the custom mapping here
    char_to_number = {
        '0': 3,
        '1': 1,
        '2': 4,
        '3': 2,
        '4': 5,
        '5': 12,
        '6': 6,
        '7': 7,
        '8': 8,
        '9': 9,
        'a': 10,
        'b': 11,
        'c': 15,
        'd': 13,
        'e': 14,
        'f': 0
    }
    

    sorted_chars = sorted(hex_string, key=lambda char: char_to_number[char])
    
    return ''.join(sorted_chars)

I want to change keep the value of f at 0 the first time it’s seen and then change it to 9 while 9 becomes 0. This is the problem I’m having. I want to do this with an if statement not a for loop because a for loop will take time to load and the rest of my code works in a way where everything needs to be instant.